AMIGA-os

The Commodore Amiga was released in 1985, and was among the first (and certainly most successful) home computers to feature a microkernel operating system. The Amiga's kernel, exec.library, was small but capable, providing fast pre-emptive multitasking on similar hardware to the cooperatively-multitasked Apple Macintosh, and an advanced dynamic linking system that allowed for easy expansion

XENIX

Xenix is a version of the Unix operating system, licensed by Microsoft from AT&T in the late 1970s. The Santa Cruz Operation (SCO) later acquired exclusive rights to the software, and eventually began distributing it as SCO UNIX.

Trusted Xenix was a variant developed by Trusted Information Systems which incorporated the Bell-LaPadula model of multilevel security, and had a multilevel secure interface for the STU-III secure communications device (that is, an STU-III connection would only be made available to applications running at the same privilege level as the key loaded in the STU-III). It was evaluated by formal methods and achieved a B2 security rating under the NSA's Trusted Computer System Evaluation Criteria—the second highest rating ever achieved by an evaluated operating system. Version 2.0 was released in January 1991, version 3.0 in April 1992, and version 4.0 in September 1993. It was still in use at least as of 1995.

EXOKERNEL

An exokernel is a type of kernel that does not abstract hardware into theoretical models. Instead it allocates physical hardware resources, such as processor time, memory pages, and disk blocks, to different programs. A program running on an exokernel can link to a library operating system that uses the exokernel to simulate the abstractions of a well-known OS, or it can develop application-specific abstractions for better performance

NANO KERNEL

A nanokernel delegates virtually all services — including even the most basic ones like interrupt controllers or the timer — to device drivers to make the kernel memory requirement even smaller than a traditional microkernel

HYBRID KERNEL

Hybrid kernels are essentially a compromise between the monolithic kernel approach and the microkernel system. This implies running some services (such as the network stack or the filesystem) in kernel space to reduce the performance overhead[citation needed] of a traditional microkernel, but still running kernel code (such as device drivers) as servers in user space

MICRO KERNEL

The microkernel approach consists of defining a simple abstraction over the hardware, with a set of primitives or system calls to implement minimal OS services such as memory management, multitasking, and inter-process communication. Other services, including those normally provided by the kernel such as networking, are implemented in user-space programs, referred to as servers. Microkernels are easier to maintain than monolithic kernels, but the large number of system calls and context switches might slow down the system because they typically generate more overhead than plain function calls.

A microkernel allows the implementation of the remaining part of the operating system as a normal application program written in a high-level language, and the use of different operating systems on top of the same unchanged kernel. It is also possible to dynamically switch among operating systems and to have more than one active simultaneously

MONOLITHIC KERNEL

In a monolithic kernel, all OS services run along with the main kernel thread, thus also residing in the same memory area. This approach provides rich and powerful hardware access. Some developers, such as UNIX developer Ken Thompson, maintain that monolithic systems are easier to design and implement than other solutions.[citation needed] The main disadvantages of monolithic kernels are the dependencies between system components - a bug in a device driver might crash the entire system - and the fact that large kernels can become very difficult to maintain.

KERNEL

In computer science, the kernel is the central component of most computer operating systems (OS). Its responsibilities include managing the system's resources (the communication between hardware and software components).[1] As a basic component of an operating system, a kernel provides the lowest-level abstraction layer for the resources (especially memory, processors and I/O devices) that application software must control to perform its function. It typically makes these facilities available to application processes through inter-process communication mechanisms and system calls.

These tasks are done differently by different kernels, depending on their design and implementation. While monolithic kernels will try to achieve these goals by executing all the code in the same address space to increase the performance of the system, microkernels run most of their services in user space, aiming to improve maintainability and modularity of the codebase.[2] A range of possibilities exists between these two extremes.

OS/2 operaing system

OS/2 is a computer operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively. The name stands for "Operating System/2," because it was introduced as part of the same generation change release as IBM's "Personal System/2 (PS/2)" line of second-generation Personal Computers. OS/2 is no longer marketed by IBM, and IBM standard support for OS/2 was discontinued on December 31, 2006.[1] Currently, Serenity Systems sells OS/2 under the brand name eComStation.

OS/2 was intended as a protected mode successor of PC-DOS and Microsoft Windows. Notably, basic system calls were modeled after MS-DOS calls; their names even started with "Dos" and it was possible to create "Family Mode" applications: text mode applications that could work on both systems.[2] Because of this heritage, OS/2 is like Windows in many ways, but it also shares similarities with Unix and Xenix.

OS/2 is also remembered for being the first major operating system to have its own advocacy group.[citation needed] Team OS/2 was a grassroots, ad-hoc organization of volunteers, who promoted and supported the operating system and applications designed for it.

IMPORTANT TIPS FOR THOSE WHO ARE USING WINDOWSXP(2)

1. It boasts how long it can stay up. Whereas previous versions of Windows were coy about how long they went between boots, XP is positively proud of its stamina. Go to the Command Prompt in the Accessories menu from the All Programs start button option, and then type 'systeminfo'. The computer will produce a lot of useful info, including the uptime. If you want to keep these, type 'systeminfo > info.txt'. This creates a file called info.txt you can look at later with Notepad. (Professional Edition only).

2. You can delete files immediately, without having them move to the Recycle Bin first. Go to the Start menu, select Run... and type 'gpedit.msc'; then select User Configuration, Administrative Templates, Windows Components, Windows Explorer and find the Do not move deleted files to the Recycle Bin setting. Set it. Poking around in gpedit will reveal a great many interface and system options, but take care -- some may stop your computer behaving as you wish. (Professional Edition only).

3. You can lock your XP workstation with two clicks of the mouse. Create a new shortcut on your desktop using a right mouse click, and enter 'rundll32.exe user32.dll,LockWorkStation' in the location field. Give the shortcut a name you like. That's it -- just double click on it and your computer will be locked. And if that's not easy enough, Windows key + L will do the same.

4. XP hides some system software you might want to remove, such as Windows Messenger, but you can tickle it and make it disgorge everything. Using Notepad or Edit, edit the text file /windows/inf/sysoc.inf, search for the word 'hide' and remove it. You can then go to the Add or Remove Programs in the Control Panel, select Add/Remove Windows Components and there will be your prey, exposed and vulnerable.

5. For those skilled in the art of DOS batch files, XP has a number of interesting new commands. These include 'eventcreate' and 'eventtriggers' for creating and watching system events, 'typeperf' for monitoring performance of various subsystems, and 'schtasks' for handling scheduled tasks. As usual, typing the command name followed by /? will give a list of options -- they're all far too baroque to go into here.

6. XP has IP version 6 support -- the next generation of IP. Unfortunately this is more than your ISP has, so you can only experiment with this on your LAN. Type 'ipv6 install' into Run... (it's OK, it won't ruin your existing network setup) and then 'ipv6 /?' at the command line to find out more. If you don't know what IPv6 is, don't worry and don't bother.

7. You can at last get rid of tasks on the computer from the command line by using 'taskkill /pid' and the task number, or just 'tskill' and the process number. Find that out by typing 'tasklist', which will also tell you a lot about what's going on in your system.

8. XP will treat Zip files like folders, which is nice if you've got a fast machine. On slower machines, you can make XP leave zip files well alone by typing 'regsvr32 /u zipfldr.dll' at the command line. If you change your mind later, you can put things back as they were by typing 'regsvr32 zipfldr.dll'.

9. XP has ClearType -- Microsoft's anti-aliasing font display technology -- but doesn't have it enabled by default. It's well worth trying, especially if you were there for DOS and all those years of staring at a screen have given you the eyes of an astigmatic bat. To enable ClearType, right click on the desktop, select Properties, Appearance, Effects, select ClearType from the second drop-down menu and enable the selection. Expect best results on laptop displays. If you want to use ClearType on the Welcome login screen as well, set the registry entry HKEY_USERS/.DEFAULT/Control Panel/Desktop/FontSmoothingType to 2.

10. You can use Remote Assistance to help a friend who's using network address translation (NAT) on a home network, but not automatically. Get your pal to email you a Remote Assistance invitation and edit the file. Under the RCTICKET attribute will be a NAT IP address, like 192.168.1.10. Replace this with your chum's real IP address -- they can find this out by going to www.whatismyip.com -- and get them to make sure that they've got port 3389 open on their firewall and forwarded to the errant computer.

GNU HURD

GNU Hurd (usually referred to as the Hurd) is a free software computer operating system kernel, released under the GNU General Public License. It has been under development since 1990 by the GNU Project of the Free Software Foundation. It consists of a set of servers (or daemons, in Unix terminology) that work on top of a microkernel; together they form the kernel of GNU. The Hurd aims to surpass Unix kernels in functionality, security, and stability, while remaining largely compatible with them.

HURD is a mutually recursive acronym, standing for HIRD of Unix-Replacing Daemons, where HIRD stands for HURD of Interfaces Representing Depth. It is also a play on the words herd of gnus, reflecting how it works.

I-PHONE OS

iPhone OS is the operating system developed by Apple Inc for the iPhone and iPod touch.[1][2] It is derived from Mac OS X, and is based on the same Mach kernel and Darwin core as Mac OS X. iPhone OS has three abstraction layers: a Core Services layer, a Media layer, and a Cocoa Touch layer. The operating system takes less than half a gigabyte (GB) of the devices' total 4–32 GB storage.[3]

Many of the function of the iPhone and iPod touch are managed through iTunes version 7.3 or later, which runs on Mac OS X version 10.4.10 or later and on 32-bit versions of Windows XP or Vista.[4] The release of iTunes 7.6 expanded this support to include 64-bit versions of Vista.[5]

NEXTSTEP

NEXTSTEP was the original object-oriented, multitasking operating system that NeXT Computer developed to run on its proprietary NeXT computers ("black boxes") such as the NeXTcube. NEXTSTEP 1.0 was released on September 18, 1989 after several previews starting in 1986. The last version, 3.3, was released in early 1995, by which time it ran not only on Motorola 68000 family processors, but also IBM PC compatible x86, Sun SPARC, and HP PA-RISC. Apple Inc.'s Mac OS X is a direct descendant of NEXTSTEP.

NEXTSTEP was a combination of several parts:

a Unix operating system based on the Mach kernel, plus source code from BSD Unix
Display PostScript and a windowing engine
the Objective-C language and runtime
an object-oriented (OO) application layer, including several "kits"
development tools for the OO layers
The key to NEXTSTEP's fame were the last three items. The toolkits offered incredible power, and were used to build all of the software on the machine. Distinctive features of the Objective-C language made the writing of applications with NEXTSTEP far easier than on many competing systems, and the system was often pointed to as a paragon of computer development, even a decade later.

NEXTSTEP's user interface was refined and consistent, and introduced the idea of the Dock, carried through OpenStep and into Mac OS X, and the Shelf. NEXTSTEP also created or was among the very first to sport a large number of other GUI concepts now common in other operating systems: 3D "chiseled" widgets, system-wide drag and drop of a wide range of objects beyond file icons, system-wide piped services, real-time scrolling and window dragging, properties dialog boxes ("inspectors"), window modification notices (such as the saved status of a file), etc. The system was among the first general-purpose user interfaces to handle publishing color standards, transparency, sophisticated sound and music processing (through a Motorola 56000 DSP), advanced graphics primitives, internationalization, and modern typography in a consistent manner across all applications.

Additional kits were added to the product line to make the system more attractive. This included Portable Distributed Objects (PDO), which allowed easy remote invocation, and Enterprise Objects Framework, a powerful object-relational database system. These kits made the system particularly interesting to custom application programmers, and NEXTSTEP had a long history in the financial programming community.

UNICOS

Unicos (officially all-caps UNICOS) is the name of a range of Unix operating system variants developed by Cray for its supercomputers. Unicos is the successor of the Cray Operating System (COS). It provides network clustering and source code compatibility layers for some other Unixes. Unicos was originally introduced in 1985 with the Cray-2 system and later ported to other Cray models. The original Unicos was based on System V.2, and had numerous BSD features (e.g., networking and file system enhancements) added to it.

CX-OS was the original name given to what is now Unicos. This was a prototype system which ran on a Cray X-MP in 1984 before the Cray-2 port. It was used to demonstrate the feasibility of using Unix on a supercomputer system, prior to the availability of Cray-2 hardware.

The operating system revamp was part of a larger movement inside Cray Research to modernize their corporate software: including rewriting their most important Fortran compiler in a higher-level language (Pascal) with more modern optimizations and vectorizations.

As a migration path for existing COS customers wishing to transition to Unicos, a Guest Operating System capability was introduced into COS. The only guest operating system that was ever supported was Unicos. A COS batch job would be submitted to start up Unicos, which would then run as a subsystem under COS - using a subset of the systems CPUs, memory, and peripheral devices. The Unicos that ran under GOS was exactly the same as when it ran stand-alone - the difference was that the kernel would make certain low-level hardware requests through the COS GOS hook, rather than directly to the hardware.

One of the sites that ran very early versions of Unicos was Bell Labs, where Unix pioneers including Dennis Ritchie ported parts of their Eighth Edition Unix (including stream I/O) to Unicos. They also experimented with a guest facility within Unicos, allowing the stand-alone version of the OS to host itself.

SUN-OS

SunOS is a version of the Unix operating system developed by Sun Microsystems for their workstation and server computer systems. The SunOS name is usually only used to refer to versions 1.0 to 4.1.4 of SunOS. These versions were based on BSD Unix, while SunOS version 5.0 and later are based on UNIX System V Release 4, and are marketed under the brand name Solaris

SunOS 1 and 2 supported the Sun-2 series systems, including Sun-1 systems upgraded with Sun-2 (68010) CPU boards. SunOS 3 supported Sun-2 and Sun-3 (68020) series systems. SunOS 4 supported Sun-2 (until release 4.0.3), Sun-3 (until 4.1.1), Sun386i (4.0, 4.0.1 and 4.0.2 only) and Sun-4 (SPARC) architectures. Although SunOS 4 was intended to be the first release to fully support Sun's new SPARC processor, there was also a SunOS 3.2 release with preliminary support for Sun-4 systems.

SunOS 4.1.2 introduced support for Sun's first sun4m-architecture multiprocessor machines (the SPARCserver 600MP series); since it had only a single lock for the kernel, only one CPU at a time could execute in the kernel.

The last release of SunOS 4 was 4.1.4 (Solaris 1.1.2) in 1994. The sun4, sun4c and sun4m architectures were supported in 4.1.4; sun4d was not supported.

Sun continued to ship SunOS 4.1.3 and 4.1.4 until December 27, 1998; they were supported until September 30, 2003.

FEATURES OF MACOS X-OPERATING SYSTEM

Aqua GUI – A fluid graphical user interface with glass-like elements. Anti-aliasing of widgets, text, graphics and window elements. ColorSync color matching built into the core drawing engine, for print and multimedia professionals. Drop shadows around window and isolated text elements to provide a sense of depth. A Dock holding file/folder shortcuts as well as minimized windows. Full-color, scalable icons up to 512x512 pixels Human interface guidelines followed by almost all applications, giving them consistent user interface and keyboard shortcuts. New interface elements including sheets (document modal dialog boxes attached to specific windows) and drawers. OpenGL composites windows onto the screen to allow hardware-accelerated drawing. This technology (introduced in version 10.2) is called Quartz Extreme. Quartz's internal imaging model correlates well with the Portable Document Format (PDF) imaging model, making it easy to output PDF to multiple devices. PDF viewing is built in. When a widget is added to the dashboard, it appears with a ripple effect.Automator – an application designed to create an automatic workflow for different tasks (introduced in version 10.4). Dashboard – A full-screen group of small applications called desktop widgets that can be called up and dismissed in one keystroke (introduced in version 10.4). Exposé – A feature which includes three functions to help accessibility between windows and desktop. Its functions are to instantly display all open windows as thumbnails for easy navigation to different tasks, display all open windows as thumbnails from the current application, and hide all windows to access the desktop (introduced in version 10.3). Finder – A file browser allowing quick access to all areas of the computer (modified throughout subsequent releases). (The Finder found in Mac OS X Jaguar had been criticized by John Siracusa for violating the concept of spatial interface.) Quick Look allows dynamic previews of files (including videos and multi-page documents) without opening their parent applications (introduced in 10.5). Spotlight search technology allows rapid real-time searches of data files, mail messages, photos, and other information, based on item properties (meta data) and/or content (introduced in version 10.4). FileVault – Optional encryption of the user's files with Advanced Encryption Standard (AES) (128-bit keys introduced in version 10.3, 256-bit keys on version 10.5). Front Row – A media viewer interface accessed by the Apple Remote (introduced in 10.4). Global application services – spell checker, special characters palette, color picker, font chooser and dictionary. Integrated Sync Services – A system which allows applications to access a centralized extensible database for various elements of user data, including calendar and contact items. The operating system manages conflicting edits and data consistency (introduced in version 10.4). Spaces – Desktop organization tool which can create and manage multiple virtual desktops and display them in an Exposé-like interface (introduced in 10.5). Cover Flow – is a three-dimensional graphical user interface included with iTunes, the Finder, and other Apple Inc. products for visually skimming through files and digital media libraries via cover artwork (introduced in 10.5). Time Machine – Automatic backup technology that allows users to view and restore previous versions of files and application data (introduced in 10.5).

Mac OS X (pronounced /mæk əʊ ɛs tɛn/[1] or Mac O-S ten) is a line of graphical operating systems developed, marketed, and sold by Apple Inc., the latest of which is pre-loaded on all currently shipping Macintosh computers. Mac OS X is the successor to the original Mac OS, which had been Apple's primary operating system since 1984.

The first version released was Mac OS X Server 1.0 in 1999, which retained the earlier Mac operating system's "platinum" appearance and even resembled OPENSTEP in places. The desktop-oriented version, Mac OS X v10.0, followed in March 2001 sporting the new Aqua user interface. Since then, five more distinct "end-user" and "server" versions have been released, most recently Mac OS X v10.5 in October 2007. Releases of Mac OS X are named after big cats; for example, Apple calls Mac OS X v10.5 "Leopard".

The server edition, Mac OS X Server, is architecturally very similar to its desktop counterpart but usually runs on Apple's line of Macintosh server hardware. It includes workgroup management and administration software tools that provide simplified access to key network services, including a mail transfer agent, a Samba server, an LDAP server, a domain name server, and others.

Apple also produces customized versions of OS X for use on three of its consumer devices, the Apple TV,[2] the iPhone and the iPod touch. The modified OS only contains what is needed for that particular device (un-needed drivers and components are removed), though certain sources have reported that simple hacks could install features in the Mac OS to the stripped down version

The most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.
For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.

Operating systems can be classified as follows:

multi-user : Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.
multiprocessing : Supports running a program on more than one CPU.
multitasking : Allows more than one program to run concurrently.
multithreading : Allows different parts of a single program to run concurrently.
real time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time.

5 ways to speed up your PC

By following a few simple guidelines, you can maintain your computer and keep it running smoothly. This article discusses how to use the tools available in Windows XP Service Pack 2 (SP2) and Windows Vista to more efficiently maintain your computer and safeguard your privacy when you're online.

Free up disk space

By freeing disk space, you can improve the performance of your computer. The Disk Cleanup tool helps you free up space on your hard disk. The utility identifies files that you can safely delete, and then enables you to choose whether you want to delete some or all of the identified files.
Use Disk Cleanup to:
• Remove temporary Internet files.
• Remove downloaded program files (such as Microsoft ActiveX controls and Java applets).
• Empty the Recycle Bin.
• Remove Windows temporary files.
• Remove optional Windows components that you don't use.
• Remove installed programs that you no longer use.

Speed up access to data

Disk fragmentation slows the overall performance of your system. When files are fragmented, the computer must search the hard disk when the file is opened to piece it back together. The response time can be significantly longer.
Disk Defragmenter is a Windows utility that consolidates fragmented files and folders on your computer's hard disk so that each occupies a single space on the disk. With your files stored neatly end-to-end, without fragmentation, reading and writing to the disk speeds up.
When to run Disk Defragmenter
In addition to running Disk Defragmenter at regular intervals—monthly is optimal—there are other times you should run it too, such as when:

•You add a large number of files.
•Your free disk space totals 15 percent or less.
•You install new programs or a new version of Windows.

Detect and repair disk errors

In addition to running Disk Cleanup and Disk Defragmenter to optimize the performance of your computer, you can check the integrity of the files stored on your hard disk by running the Error Checking utility.
As you use your hard drive, it can develop bad sectors. Bad sectors slow down hard disk performance and sometimes make data writing (such as file saving) difficult, or even impossible. The Error Checking utility scans the hard drive for bad sectors, and scans for file system errors to see whether certain files or folders are misplaced.
If you use your computer daily, you should run this utility once a week to help prevent data loss.

Protect your computer against spyware

Spyware collects personal information without letting you know and without asking for permission. From the Web sites you visit to usernames and passwords, spyware can put you and your confidential information at risk. In addition to privacy concerns, spyware can hamper your computer's performance. To combat spyware, you might want to consider using Microsoft Windows Defender, which is included in Windows Vista, and is available as a free download for Microsoft XP SP2. Alternatively, there are other free anti-spyware software programs available.

Learn all about ReadyBoost

If you're using Windows Vista, you can use ReadyBoost to speed up your system. A new concept in adding memory to a system, it allows you to use non-volatile flash memory—like a USB flash drive or a memory card—to improve performance without having to add additional memory.

cp/m operating system

CP/M is an operating system originally created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc. Initially confined to single tasking on 8-bit processors and no more than 64 kilobytes (64 KiB) of memory, later versions of CP/M added multi-user variations, and were migrated to 16-bit processors.

The combination of CP/M and S-100 bus computers patterned on the MITS Altair was an early "industry standard" for microcomputers, and was widely used through the late 1970s and into the mid-'80s. By greatly reducing the amount of programming required to install an application on a new manufacturer's computer, CP/M increased the market size for both hardware and software.

WINDOWS98

Windows 98 (codenamed Memphis) is a graphical operating system released on June 25, 1998 by Microsoft and the successor to Windows 95. Like its predecessor, it is a hybrid 16-bit/32-bit monolithic product based on MS-DOS.

The first edition of Windows 98 is designated by the internal version number 4.10.1998, or 4.10.1998A if it has been updated with the Security CD from Microsoft. Windows 98 Second Edition is designated by the internal version number 4.10.2222A, or 4.10.2222B if it has been updated with the Security CD from Microsoft. Windows 98 was succeeded by Windows Me on September 14, 2000.

DOS(disk operating system)

In July 1980 IBM assigned Microsoft to develop a 16-bit operating system for the personal computer for the fee of 186,000 dollars. Although the company Digital Research of Gary Kildall allready had with CP/M 86 such a 16-bit version,but by circumstances no contract has been established with IBM. Microsoft did not have yet any operating system, Microsoft licensed CP/M from Digital Research in November 1977 for 50,000 dollars. Since Microsoft could not sell licenses, a corresponding agreement with the company Seattle Computer Products was reached for QDOS. QDOS is a 16-bit clone of CP/M and was finished by Tim Paterson in April 1980. At first Microsoft licensed QDOS for 25,000 dollars. After a licence agreement with IBM was signed, Bill Gates bought QDOS for 50,000 dollars in July 1981. How proved this was a very lucrative business. IBM delivered it on all IBM computers as PC DOS for the first time on the IBM 5150 PC, for all other ones the name MS-DOS was for OEM partner. MS DOS 1.0 consists of about 4,000 lines assembler code.

The command interpreter is integrated in the file command.com with the internal commands for MS-DOS. Together with the file io.sys for simple device routines like the access to the monitor, keyboard, fixed storage disks and interfaces as well as the booting code these form the base operating system. DOS works very hardware near.

In 1982 MS-DOS becomes the binary standard for all compatible systems when 50 companies licensed MS-DOS. Software and hardware manufacturers build on this standard at this time. In 1983 the success of the PC system was clear the desire for a graphical surface was rising. Microsoft corresponded to the trend and announced a graphical user interface named Windows in 1983. Many other systems lost her market relevance at this time. In 1984 the number of PC and MS-DOS resellers increased to over 200. IBM published the AT computer in August, this one should refine the market for personal computer with MS-DOS 3.0/3.1. MS-DOS is already spread worldwide on Intel x86 computers in 1985. The easy extendibility of the computer by numerous plug-in cards of third party manufacturers, relatively low acquisition costs and a strongly growing amount of applications was a reason for it.

1988 was MS-DOS established and had reached measured on the market share a monopoly in the DOS market. The number of the MS-DOS installations grew worldwide to about 60 million and surpassed all other systems with that amount. Almost every software company offered standard applications like word processing, calculation or also special solutions like measurement tools, CAD (Computer Aided Design) or image processing for MS-DOS. The PC manufacturers designed her systems compatible to MS-DOS except for few manufacturers.

mach

Mach (kernel)

Mach is an operating system microkernel developed at Carnegie Mellon University to support operating system research, primarily distributed and parallel computation. It is one of the earliest examples of a microkernel, and still the standard by which similar projects are measured.

The project at Carnegie Mellon ran from 1985 to 1994, ending with Mach 3.0. A number of other efforts have continued Mach research, including the University of Utah's Mach 4. Mach was developed as a replacement for the kernel in the BSD version of UNIX, so no new operating system would have to be designed around it. Today further experimental research on Mach appears ended, although Mach and its derivatives are in use in a number of commercial operating systems, such as NEXTSTEP and OPENSTEP, and most notably Mac OS X (using the XNU kernel). The Mach VM system was also adopted by the BSD developers at CSRG, and appears in modern BSD-derived UNIX systems, such as FreeBSD. Neither Mac OS X nor FreeBSD maintain the microkernel structure pioneered in Mach, although Mac OS X continues to offer microkernel Inter-Process Communication and control primitives for use directly by applications.

Mach is the logical successor to Carnegie Mellon's Accent kernel. The lead developer on the Mach project, Richard Rashid, has been working at Microsoft since 1991 in various top-level positions revolving around the Microsoft Research division. Another of the original Mach developers, Avie Tevanian, was formerly head of software at NeXT, then Chief Software Technology Officer at Apple Computer until March 2006.

solaris

Solaris Operating System

Solaris 10 using Java Desktop System
developer Sun Microsystems
OS family Unix
Source model Mixed open source / closed source
Latest stable release 10 8/07 / 4 September 2007
Supported platforms SPARC, x86, x86-64
Kernel type Monolithic kernel
Default user interface Java Desktop System or CDE
License Proprietary software
Working state Current
The Solaris Operating System, usually known simply as Solaris, is a Unix-based operating system introduced by Sun Microsystems in 1992 as the successor to SunOS.

Solaris is known for its scalability, especially on SPARC systems, as well for being the origin for many innovative features such as DTrace and ZFS. Solaris supports SPARC-based and x86-based workstations and servers from Sun and other vendors, with efforts underway to port to additional platforms.

Solaris is certified against the Single Unix Specification. Although it was historically developed as proprietary software, a majority of its codebase is now open source software as OpenSolaris.

unix

unix

Filiation of Unix and Unix-like systemsUnix (officially trademarked as UNIX®, sometimes also written as Unix or Unix® with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. Today's Unix systems are split into various branches, developed over time by AT&T as well as various commercial vendors and non-profit organizations.

As of 2007, the owner of the trademark UNIX® is The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX®" (others are called "Unix system-like" or "Unix-like").

During the late 1970s and early 1980s, Unix's influence in academic circles led to large-scale adoption of Unix (particularly of the BSD variant, originating from the University of California, Berkeley) by commercial startups, the most notable of which is Sun Microsystems. Today, in addition to certified Unix systems, Unix-like operating systems such as Linux and BSD are commonly encountered. Sometimes, "traditional Unix" may be used to describe a Unix or an operating system that has the characteristics of either Version 7 Unix or UNIX System V.

Contents [hide]
1 Overview
2 History
2.1 1970s
2.2 1980s
2.3 1990s
2.4 2000 to present
3 Standards
4 Components
5 Impact
5.1 2038
6 Free Unix-like operating systems
7 Branding
8 Common Unix commands
9 References
10 External links



[edit] Overview
Unix operating systems are widely used in both servers and workstations. The Unix environment and the client-server program model were essential elements in the development of the Internet and the reshaping of computing as centered in networks rather than in individual computers.

Both Unix and the C programming language were developed by AT&T and distributed to government and academic institutions, causing both to be ported to a wider variety of machine families than any other operating system. As a result, Unix became synonymous with "open systems".

Unix was designed to be portable, multi-tasking and multi-user in a time-sharing configuration. Unix systems are characterized by various concepts: the use of plain text for storing data; a hierarchical file system; treating devices and certain types of inter-process communication (IPC) as files; and the use of a large number of small programs that can be strung together through a command line interpreter using pipes, as opposed to using a single monolithic program that includes all of the same functionality. These concepts are known as the Unix philosophy.

Under Unix, the "operating system" consists of many of these utilities along with the master control program, the kernel. The kernel provides services to start and stop programs, handle the file system and other common "low level" tasks that most programs share, and, perhaps most importantly, schedules access to hardware to avoid conflicts if two programs try to access the same resource or device simultaneously. To mediate such access, the kernel was given special rights on the system, leading to the division between user-space and kernel-space.

The microkernel tried to reverse the growing size of kernels and return to a system in which most tasks were completed by smaller utilities. In an era when a "normal" computer consisted of a hard disk for storage and a data terminal for input and output (I/O), the Unix file model worked quite well as most I/O was "linear". However, modern systems include networking and other new devices. Describing a graphical user interface driven by mouse control in an "event driven" fashion didn't work well under the old model. Work on systems supporting these new devices in the 1980s led to facilities for non-blocking I/O, forms of inter-process communications other than just pipes, as well as moving functionality such as network protocols out of the kernel.


[edit] History

A partial list of simultaneously running processes on a Unix system.In the 1960s, the Massachusetts Institute of Technology, AT&T Bell Labs, and General Electric worked on an experimental operating system called Multics (Multiplexed Information and Computing Service), which was designed to run on the GE-645 mainframe computer. (Eventually this became a commercial product, although sales did not meet expectations.) Multics was an interactive operating system with many novel capabilities, including enhanced security.

AT&T Bell Labs pulled out of the Multics project and deployed its resources elsewhere. One of the developers on the Bell Labs team, Ken Thompson, continued to develop for the GE-645 mainframe, and wrote a game for that computer called Space Travel.[1] However, he found that the game was too slow on the GE machine and was expensive, costing $75 per execution in scarce computing time.[2]

Thompson thus re-wrote the game in assembly language for Digital Equipment Corporation's PDP-7 with help from Dennis Ritchie. This experience, combined with his work on the Multics project, led Thompson to start a new operating system for the PDP-7. Thompson and Ritchie led a team of developers, including Rudd Canaday, at Bell Labs developing a file system as well as the new multi-tasking operating system itself. They included a command line interpreter and some small utility programs.[3]


Editing a shell script using the ed editor. The dollar-sign at the top of the screen is the prompt printed by the shell. 'ed' is typed to start the editor, which takes over from that point on the screen downwards.
[edit] 1970s
In the 1970s the project was named Unics, and eventually could support two simultaneous users. Brian Kernighan invented this name as a contrast to Multics; the spelling was later changed to Unix.

Up until this point there had been no financial support from Bell Labs. When the Computer Science Research Group wanted to use Unix on a much larger machine than the PDP-7, Thompson and Ritchie managed to trade the promise of adding text processing capabilities to Unix for a PDP-11/20 machine. This led to some financial support from Bell. For the first time in 1970, the Unix operating system was officially named and ran on the PDP-11/20. It added a text formatting program called roff and a text editor. All three were written in PDP-11/20 assembly language. Bell Labs used this initial "text processing system", made up of Unix, roff, and the editor, for text processing of patent applications. Roff soon evolved into troff, the first electronic publishing program with a full typesetting capability. The UNIX Programmer's Manual was published on November 3, 1971.

In 1973, Unix was rewritten in the C programming language, contrary to the general notion at the time "that something as complex as an operating system, which must deal with time-critical events, had to be written exclusively in assembly language".[4] The migration from assembly language to the higher-level language C resulted in much more portable software, requiring only a relatively small amount of machine-dependent code to be replaced when porting Unix to other computing platforms.

AT&T made Unix available to universities and commercial firms, as well as the United States government under licenses. The licenses included all source code including the machine-dependent parts of the kernel, which were written in PDP-11 assembly code. Copies of the annotated Unix kernel sources circulated widely in the late 1970s in the form of a much-copied book by John Lions of the University of New South Wales, the Lions' Commentary on UNIX 6th Edition, with Source Code, which led to considerable use of Unix as an educational example.

Versions of the Unix system were determined by editions of its user manuals, so that (for example) "Fifth Edition UNIX" and "UNIX Version 5" have both been used to designate the same thing. Development expanded, with Versions 4, 5, and 6 being released by 1975. These versions added the concept of pipes, leading to the development of a more modular code-base, increasing development speed still further. Version 5 and especially Version 6 led to a plethora of different Unix versions both inside and outside Bell Labs, including PWB/UNIX, IS/1 (the first commercial Unix), and the University of Wollongong's port to the Interdata 7/32 (the first non-PDP Unix).

In 1978, UNIX/32V, for DEC's then new VAX system, was released. By this time, over 600 machines were running Unix in some form. Version 7 Unix, the last version of Research Unix to be released widely, was released in 1979. Versions 8, 9 and 10 were developed through the 1980s but were only released to a few universities, though they did generate papers describing the new work. This research led to the development of Plan 9 from Bell Labs, a new portable distributed system.


[edit] 1980s

A late-80s style Unix desktop running the X Window System graphical user interface. Shown are a number of client applications common to the MIT X Consortium's distribution, including Tom's Window Manager, an X Terminal, Xbiff, xload, and a graphical manual page browser.AT&T licensed UNIX System III, based largely on Version 7, for commercial use, the first version launching in 1982. This also included support for the VAX. AT&T continued to issue licenses for older Unix versions. To end the confusion between all its differing internal versions, AT&T combined them into UNIX System V Release 1. This introduced a few features such as the vi editor and curses from the Berkeley Software Distribution of Unix developed at the University of California, Berkeley. This also included support for the Western Electric 3B series of machines.

Since the newer commercial UNIX licensing terms were not as favorable for academic use as the older versions of Unix, the Berkeley researchers continued to develop BSD Unix as an alternative to UNIX System III and V, originally on the PDP-11 architecture (the 2.xBSD releases, ending with 2.11BSD) and later for the VAX-11 (the 4.x BSD releases). Many contributions to Unix first appeared on BSD releases, notably the C shell with job control (modelled on ITS). Perhaps the most important aspect of the BSD development effort was the addition of TCP/IP network code to the mainstream Unix kernel. The BSD effort produced several significant releases that contained network code: 4.1cBSD, 4.2BSD, 4.3BSD, 4.3BSD-Tahoe ("Tahoe" being the nickname of the Computer Consoles Inc. Power 6/32 architecture that was the first non-DEC release of the BSD kernel), Net/1, 4.3BSD-Reno (to match the "Tahoe" naming, and that the release was something of a gamble), Net/2, 4.4BSD, and 4.4BSD-lite. The network code found in these releases is the ancestor of much TCP/IP network code in use today, including code that was later released in AT&T System V UNIX and early versions of Microsoft Windows. The accompanying Berkeley Sockets API is a de facto standard for networking APIs and has been copied on many platforms.

Other companies began to offer commercial versions of the UNIX System for their own mini-computers and workstations. Most of these new Unix flavors were developed from the System V base under a license from AT&T; however, others were based on BSD instead. One of the leading developers of BSD, Bill Joy, went on to co-found Sun Microsystems in 1982 and created SunOS (now Solaris) for their workstation computers. In 1980, Microsoft announced its first Unix for 16-bit microcomputers called Xenix, which the Santa Cruz Operation (SCO) ported to the Intel 8086 processor in 1983, and eventually branched Xenix into SCO UNIX in 1989.

For a few years during this period (before PC compatible computers with MS-DOS became dominant), industry observers expected that UNIX, with its portability and rich capabilities, was likely to become the industry standard operating system for microcomputers.[5] In 1984 several companies established the X/Open consortium with the goal of creating an open system specification based on UNIX. Despite early progress, the standardization effort collapsed into the "Unix wars," with various companies forming rival standardization groups. The most successful Unix-related standard turned out to be the IEEE's POSIX specification, designed as a compromise API readily implemented on both BSD and System V platforms, published in 1988 and soon mandated by the United States government for many of its own systems.

AT&T added various features into UNIX System V, such as file locking, system administration, streams, new forms of IPC, the Remote File System and TLI. AT&T cooperated with Sun Microsystems and between 1987 and 1989 merged features from Xenix, BSD, SunOS, and System V into System V Release 4 (SVR4), independently of X/Open. This new release consolidated all the previous features into one package, and heralded the end of competing versions. It also increased licensing fees.

During this time a number of vendors including Digital Equipment, Sun, Addamax and others began building trusted versions of UNIX for high security applications, mostly designed for military and law enforcement applications.


The Common Desktop Environment or CDE, a graphical desktop for Unix co-developed in the 1990s by HP, IBM, and Sun as part of the COSE initiative.
[edit] 1990s
In 1990, the Open Software Foundation released OSF/1, their standard Unix implementation, based on Mach and BSD. The Foundation was started in 1988 and was funded by several Unix-related companies that wished to counteract the collaboration of AT&T and Sun on SVR4. Subsequently, AT&T and another group of licensees formed the group "UNIX International" in order to counteract OSF. This escalation of conflict between competing vendors gave rise again to the phrase "Unix wars".

In 1991, a group of BSD developers (Donn Seeley, Mike Karels, Bill Jolitz, and Trent Hein) left the University of California to found Berkeley Software Design, Inc (BSDI). BSDI produced a fully functional commercial version of BSD Unix for the inexpensive and ubiquitous Intel platform, which started a wave of interest in the use of inexpensive hardware for production computing. Shortly after it was founded, Bill Jolitz left BSDI to pursue distribution of 386BSD, the free software ancestor of FreeBSD, OpenBSD, and NetBSD.

By 1993 most commercial vendors had changed their variants of Unix to be based on System V with many BSD features added on top. The creation of the COSE initiative that year by the major players in Unix marked the end of the most notorious phase of the Unix wars, and was followed by the merger of UI and OSF in 1994. The new combined entity, which retained the OSF name, stopped work on OSF/1 that year. By that time the only vendor using it was Digital, which continued its own development, rebranding their product Digital UNIX in early 1995.

Shortly after UNIX System V Release 4 was produced, AT&T sold all its rights to UNIX to Novell. (Dennis Ritchie likened this to the Biblical story of Esau selling his birthright for the proverbial "mess of pottage".[6]) Novell developed its own version, UnixWare, merging its NetWare with UNIX System V Release 4. Novell tried to use this to battle against Windows NT, but their core markets suffered considerably.

In 1993, Novell decided to transfer the UNIX® trademark and certification rights to the X/Open Consortium.[7] In 1996, X/Open merged with OSF, creating the Open Group. Various standards by the Open Group now define what is and what is not a "UNIX" operating system, notably the post-1998 Single UNIX Specification.

In 1995, the business of administering and supporting the existing UNIX licenses, plus rights to further develop the System V code base, were sold by Novell to the Santa Cruz Operation.[1] Whether Novell also sold the copyrights is currently the subject of litigation (see below).

In 1997, Apple Computer sought out a new foundation for its Macintosh operating system and chose NEXTSTEP, an operating system developed by NeXT. The core operating system, which was based on BSD and the Mach kernel, was renamed Darwin after Apple acquired it. The deployment of Darwin in Mac OS X makes it, according to a statement made by an Apple employee at a USENIX conference, the most widely used Unix-based system in the desktop computer market.


[edit] 2000 to present
See also: SCO-Linux controversies

A modern Unix desktop environment (Solaris 10)In 2000, SCO sold its entire UNIX business and assets to Caldera Systems, which later on changed its name to The SCO Group. This new player then started legal action against various users and vendors of Linux. SCO have alleged that Linux contains copyrighted Unix code now owned by The SCO Group. Other allegations include trade-secret violations by IBM, or contract violations by former Santa Cruz customers who have since converted to Linux. However, Novell disputed the SCO group's claim to hold copyright on the UNIX source base. According to Novell, SCO (and hence the SCO Group) are effectively franchise operators for Novell, which also retained the core copyrights, veto rights over future licensing activities of SCO, and 95% of the licensing revenue. The SCO Group disagreed with this, and the dispute resulted in the SCO v. Novell lawsuit.

In 2005, Sun Microsystems released the bulk of its Solaris system code (based on UNIX System V Release 4) into an open source project called OpenSolaris. New Sun OS technologies such as the ZFS file system are now first released as open source code via the OpenSolaris project; as of 2006 it has spawned several non-Sun distributions such as SchilliX, Belenix, Nexenta and MarTux.

The Dot-com crash has led to significant consolidation of Unix projects. Of the many commercial flavors of Unix that were born in the 1980s, only Solaris, HP-UX, and AIX are still doing relatively well in the market, though SGI's IRIX persisted for quite some time. Of these, Solaris has the most market share.[8]


[edit] Standards
Beginning in the late 1980s, an open operating system standardization effort now known as POSIX provided a common baseline for all operating systems; IEEE based POSIX around the common structure of the major competing variants of the Unix system, publishing the first POSIX standard in 1988. In the early 1990s a separate but very similar effort was started by an industry consortium, the Common Open Software Environment (COSE) initiative, which eventually became the Single UNIX Specification administered by The Open Group). Starting in 1998 the Open Group and IEEE started the Austin Group, to provide a common definition of POSIX and the Single UNIX Specification.

In an effort towards compatibility, in 1999 several Unix system vendors agreed on SVR4's Executable and Linkable Format (ELF) as the standard for binary and object code files. The common format allows substantial binary compatibility among Unix systems operating on the same CPU architecture.

The Filesystem Hierarchy Standard was created to provide a reference directory layout for Unix-like operating systems, particularly Linux.


[edit] Components
See also: list of Unix programs
The Unix system is composed of several components that are normally packaged together. By including — in addition to the kernel of an operating system — the development environment, libraries, documents, and the portable, modifiable source-code for all of these components, Unix was a self-contained software system. This was one of the key reasons it emerged as an important teaching and learning tool and has had such a broad influence.

The inclusion of these components did not make the system large — the original V7 UNIX distribution, consisting of copies of all of the compiled binaries plus all of the source code and documentation occupied less than 10MB, and arrived on a single 9-track magtape. The printed documentation, typeset from the on-line sources, was contained in two volumes.

The names and filesystem locations of the Unix components has changed substantially across the history of the system. Nonetheless, the V7 implementation is considered by many to have the canonical early structure:

Kernel — source code in /usr/sys, composed of several sub-components:
conf — configuration and machine-dependent parts, including boot code
dev — device drivers for control of hardware (and some pseudo-hardware)
sys — operating system "kernel", handling memory management, process scheduling, system calls, etc.
h — header files, defining key structures within the system and important system-specific invariables
Development Environment — Early versions of Unix contained a development environment sufficient to recreate the entire system from source code:
cc — C language compiler (first appeared in V3 Unix)
as — machine-language assembler for the machine
ld — linker, for combining object files
lib — object-code libraries (installed in /lib or /usr/lib) libc, the system library with C run-time support, was the primary library, but there have always been additional libraries for such things as mathematical functions (libm) or database access. V7 Unix introduced the first version of the modern "Standard I/O" library stdio as part of the system library. Later implementations increased the number of libraries significantly.
make - build manager (introduced in PWB/UNIX), for effectively automating the build process
include — header files for software development, defining standard interfaces and system invariants
Other languages — V7 Unix contained a Fortran-77 compiler, a programmable arbitrary-precision calculator (bc, dc), and the awk "scripting" language, and later versions and implementations contain many other language compilers and toolsets. Early BSD releases included Pascal tools, and many modern Unix systems also include the GNU Compiler Collection as well as or instead of a proprietary compiler system.
Other tools — including an object-code archive manager (ar), symbol-table lister (nm), compiler-development tools (e.g. lex & yacc), and debugging tools.
Commands — Unix makes little distinction between commands (user-level programs) for system operation and maintenance (e.g. cron), commands of general utility (e.g. grep), and more general-purpose applications such as the text formatting and typesetting package. Nonetheless, some major categories are:
sh — The "shell" programmable command-line interpreter, the primary user interface on Unix before window systems appeared, and even afterward (within a "command window").
Utilities — the core tool kit of the Unix command set, including cp, ls, grep, find and many others. Subcategories include:
System utilities — administrative tools such as mkfs, fsck, and many others
User utilities — environment management tools such as passwd, kill, and others.
Document formatting — Unix systems were used from the outset for document preparation and typesetting systems, and included many related programs such as nroff, troff, tbl, eqn, refer, and pic. Some modern Unix systems also include packages such as TeX and Ghostscript.
Graphics — The plot subsystem provided facilities for producing simple vector plots in a device-independent format, with device-specific interpreters to display such files. Modern Unix systems also generally include X11 as a standard windowing system and GUI, and many support OpenGL.
Communications — Early Unix systems contained no inter-system communication, but did include the inter-user communication programs mail and write. V7 introduced the early inter-system communication system UUCP, and systems beginning with BSD release 4.1c included TCP/IP utilities.

The 'man' command can display a 'man page' for every command on the system, including itself.Documentation — Unix was the first operating system to include all of its documentation online in machine-readable form. The documentation included:
man — manual pages for each command, library component, system call, header file, etc.
doc — longer documents detailing major subsystems, such as the C language and troff

[edit] Impact
The Unix system had significant impact on other operating systems.

It was written in high level language as opposed to assembly language (which had been thought necessary for systems implementation on early computers). Although this followed the lead of Multics and Burroughs, it was Unix that popularized the idea.

Unix had a drastically simplified file model compared to many contemporary operating systems, treating all kinds of files as simple byte arrays. The file system hierarchy contained machine services and devices (such as printers, terminals, or disk drives), providing a uniform interface, but at the expense of occasionally requiring additional mechanisms such as ioctl and mode flags to access features of the hardware that did not fit the simple "stream of bytes" model. The Plan 9 operating system pushed this model even further and eliminated the need for additional mechanisms.

Unix also popularized the hierarchical file system with arbitrarily nested subdirectories, originally introduced by Multics. Other common operating systems of the era had ways to divide a storage device into multiple directories or sections, but they had a fixed number of levels, often only one level. Several major proprietary operating systems eventually added recursive subdirectory capabilities also patterned after Multics. DEC's RSX-11M's "group, user" hierarchy evolved into VMS directories, CP/M's volumes evolved into MS-DOS 2.0+ subdirectories, and HP's MPE group.account hierarchy and IBM's SSP and OS/400 library systems were folded into broader POSIX file systems.

Making the command interpreter an ordinary user-level program, with additional commands provided as separate programs, was another Multics innovation popularized by Unix. The Unix shell used the same language for interactive commands as for scripting (shell scripts — there was no separate job control language like IBM's JCL). Since the shell and OS commands were "just another program", the user could choose (or even write) his own shell. New commands could be added without changing the shell itself. Unix's innovative command-line syntax for creating chains of producer-consumer processes (pipelines) made a powerful programming paradigm (coroutines) widely available. Many later command-line interpreters have been inspired by the Unix shell.

A fundamental simplifying assumption of Unix was its focus on ASCII text for nearly all file formats. There were no "binary" editors in the original version of Unix — the entire system was configured using textual shell command scripts. The common denominator in the I/O system was the byte — unlike "record-based" file systems. The focus on text for representing nearly everything made Unix pipes especially useful, and encouraged the development of simple, general tools that could be easily combined to perform more complicated ad hoc tasks. The focus on text and bytes made the system far more scalable and portable than other systems. Over time, text-based applications have also proven popular in application areas, such as printing languages (PostScript), and at the application layer of the Internet Protocols, e.g. Telnet, FTP, SSH, SMTP, HTTP and SIP.

Unix popularized a syntax for regular expressions that found widespread use. The Unix programming interface became the basis for a widely implemented operating system interface standard (POSIX, see above).

The C programming language soon spread beyond Unix, and is now ubiquitous in systems and applications programming.

Early Unix developers were important in bringing the theory of modularity and reusability into software engineering practice, spawning a "Software Tools" movement.

Unix provided the TCP/IP networking protocol on relatively inexpensive computers, which contributed to the Internet explosion of world-wide real-time connectivity, and which formed the basis for implementations on many other platforms. (This also exposed numerous security holes in the networking implementations.)

The Unix policy of extensive on-line documentation and (for many years) ready access to all system source code raised programmer expectations, and contributed to the 1983 launch of the free software movement.

Over time, the leading developers of Unix (and programs that ran on it) evolved a set of cultural norms for developing software, norms which became as important and influential as the technology of Unix itself; this has been termed the Unix philosophy.


[edit] 2038
Main article: Year 2038 problem
Unix stores system time values as the number of seconds from midnight January 1, 1970 (the "Unix Epoch") in variables of type time_t, historically defined as "signed 32-bit integer". On January 19, 2038, the current time will roll over from a zero followed by 31 ones (01111111111111111111111111111111) to a one followed by 31 zeros (10000000000000000000000000000000), which will reset time to the year 1901 or 1970, depending on implementation, because that toggles the sign bit. As many applications use OS library routines for date calculations, the impact of this could be felt much earlier than 2038; for instance, 30-year mortgages may be calculated incorrectly beginning in the year 2008.

Since times before 1970 are rarely represented in Unix time, one possible solution that is compatible with existing binary formats would be to redefine time_t as "unsigned 32-bit integer". However, such a kludge merely postpones the problem to February 7, 2106, and could introduce bugs in software that compares differences between two sets of time.

Some Unix versions have already addressed this. For example, in Solaris on 64-bit systems, time_t is 64 bits long, meaning that the OS itself and 64-bit applications will correctly handle dates for some 292 billion years (several times greater than the age of the universe). Existing 32-bit applications using a 32-bit time_t continue to work on 64-bit Solaris systems but are still prone to the 2038 problem.


[edit] Free Unix-like operating systems

Linux is a modern Unix-like systemIn 1983, Richard Stallman announced the GNU project, an ambitious effort to create a free software Unix-like system; "free" in that everyone who received a copy would be free to use, study, modify, and redistribute it. GNU's goal was achieved in 1992. Its own kernel development project, GNU Hurd, had not produced a working kernel, but a compatible kernel called Linux was released as free software in 1992 under the GNU General Public License. The combination of the two is frequently referred to simply as "Linux", although the Free Software Foundation and some Linux distributions, such as Debian GNU/Linux, use the combined term GNU/Linux.

In addition to their use in the Linux operating system, many GNU packages — such as the GNU Compiler Collection (and the rest of the GNU toolchain), the GNU C library and the GNU core utilities — have gone on to play central roles in other free Unix systems as well.

Linux distributions, comprising Linux and large collections of compatible software have become popular both with hobbyists and in business. Popular distributions include Red Hat Enterprise Linux, Fedora, SUSE Linux Enterprise, openSUSE, Debian GNU/Linux, Ubuntu, Mandriva Linux, Slackware Linux and Gentoo.

A free derivative of BSD Unix, 386BSD, was also released in 1992 and led to the NetBSD and FreeBSD projects. With the 1994 settlement of a lawsuit that UNIX Systems Laboratories brought against the University of California and Berkeley Software Design Inc. (USL v. BSDi), it was clarified that Berkeley had the right to distribute BSD Unix — for free, if it so desired. Since then, BSD Unix has been developed in several different directions, including OpenBSD and DragonFly BSD.

Linux and BSD are now rapidly occupying much of the market traditionally occupied by proprietary Unix operating systems, as well as expanding into new markets such as the consumer desktop and mobile and embedded devices. Due to the modularity of the Unix design, sharing bits and pieces is relatively common; consequently, most or all Unix and Unix-like systems include at least some BSD code, and modern systems also typically include some GNU utilities in their distribution.

In 2005, Sun Microsystems released the bulk of the source code to the Solaris operating system, a System V variant, under the name OpenSolaris, making it the first actively developed commercial Unix system to be open sourced (several years earlier, Caldera had released many of the older Unix systems under an educational and later BSD license). As a result, a great deal of formerly proprietary AT&T/USL code is now freely available.


[edit] Branding
See also: list of Unix systems
In October 1993, Novell, the company that owned the rights to the Unix System V source at the time, transferred the trademarks of Unix to the X/Open Company (now The Open Group),[9] and in 1995 sold the related business operations to Santa Cruz Operation.[10] Whether Novell also sold the copyrights to the actual software was the subject of a 2006 federal lawsuit, SCO v. Novell, which Novell won; the case is being appealed.[citation needed] Unix vendor SCO Group Inc. accused Novell of slander of title.

The present owner of the trademark UNIX® is The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX®" (others are called "Unix system-like" or "Unix-like").

By decree of The Open Group, the term "UNIX®" refers more to a class of operating systems than to a specific implementation of an operating system; those operating systems which meet The Open Group's Single UNIX Specification should be able to bear the UNIX® 98 or UNIX® 03 trademarks today, after the operating system's vendor pays a fee to The Open Group. Systems licensed to use the UNIX® trademark include AIX, HP-UX, IRIX, Solaris, Tru64 (formerly "Digital UNIX"), A/UX, Mac OS X 10.5 on Intel platforms,[11] and a part of z/OS.

Sometimes a representation like "Un*x", "*NIX", or "*N?X" is used to indicate all operating systems similar to Unix. This comes from the use of the "*" and "?" characters as "wildcard" characters in many utilities. This notation is also used to describe other Unix-like systems, e.g. Linux, BSD, etc., that have not met the requirements for UNIX® branding from the Open Group.

The Open Group requests that "UNIX®" is always used as an adjective followed by a generic term such as "system" to help avoid the creation of a genericized trademark.

"Unix" was the original formatting, but the usage of "UNIX" remains widespread because, according to Dennis Ritchie, when presenting the original Unix paper to the third Operating Systems Symposium of the American Association for Computing Machinery, “we had a new typesetter and troff had just been invented and we were intoxicated by being able to produce small caps.”[12]. Many of the operating system's predecessors and contemporaries used all-uppercase lettering, so many people wrote the name in upper case due to force of habit.

Several plural forms of Unix are used to refer to multiple brands of Unix and Unix-like systems. Most common is the conventional "Unixes", but the hacker culture which created Unix has a penchant for playful use of language, and "Unices" (treating Unix as Latin noun of the third declension) is also popular. The Anglo-Saxon plural form "Unixen" is not common, although occasionally seen. Trademark names can be registered by different entities in different countries and trademark laws in some countries allow the same trademark name to be controlled by two different entities if each entity uses the trademark in easily distinguishable categories. The result is that Unix has been used as a brand name for various products including book shelves, ink pens, bottled glue, diapers, hair driers and food containers. [2].


[edit] Common Unix commands
Wikibooks Guide to Unix has a page on the topic of
CommandsSee also: List of Unix utilities
Widely used Unix commands include:

Directory and file creation and navigation: ls cd pwd mkdir rm rmdir cp find touch mv
File viewing and editing: more less ed vi emacs head tail
Text processing: echo cat grep sort uniq sed awk cut tr split printf
File comparison: comm cmp diff patch
Miscellaneous shell tools: yes test xargs
System administration: chmod chown ps su w who
Communication: mail telnet ftp finger ssh
Authentication: su login passwd

[edit] References
^ Ritchie, Dennis M.. Space Travel: Exploring the solar system and the PDP-7. Retrieved on 2007-03-11.
^ http://www.bell-labs.com/history/unix/pdp7.html
^ http://www.bell-labs.com/history/unix/takeshape.html
^ Stallings, William. "Operating Systems: Internals and Design Principles" 5th ed, page 91. Pearson Education, Inc. 2005.
^ "UNIX". The Computer Chronicles. 1985.
^ http://groups.google.com/group/comp.unix.questions/browse_frm/thread/2f0b5e719fa3a3ec/3fa5e5fe4d58f96b
^ http://groups.google.com/group/comp.std.unix/msg/c9974cf0022884f8
^ Stephen Shankland (December 7, 2005). Itanium: A cautionary tale. Tech News. ZDNet. Retrieved on 2006-10-04. “In the third quarter of this year, 7,845 Itanium servers were sold, according to research by Gartner. That compares with 62,776 machines with Sun Microsystems' UltraSparc, 31,648 with IBM's Power, and 9,147 with HP's PA-RISC.”
^ http://groups.google.com/group/comp.std.unix/msg/c9974cf0022884f8
^ http://www.novell.com/news/press/archive/1995/09/pr95220.html
^ The Open Group. Mac OS X Version 10.5 Leopard on Intel-based Macintosh computers certification. Retrieved on 2007-06-12.
^ http://catb.org/jargon/html/U/Unix.html
Ritchie, D.M.; Thompson, K., The UNIX Time-Sharing System (The Bell System Technical Journal, July-August 1978, Vol. 57, No. 6, Part 2)
Salus, Peter H.: A Quarter Century of UNIX, Addison Wesley, June 1, 1994; ISBN 0-201-54777-5
UNIX History. www.levenez.com. Retrieved on 17 March, 2005.
AIX, FreeBSD, HP-UX, Linux, Solaris, Tru64. UNIXguide.net. Retrieved on 17 March, 2005.
Linux Weekly News, February 21, 2002. lwn.net. Retrieved on 7 April, 2006.
Lions, John: Lions' Commentary on the Sixth Edition UNIX Operating System. with Source Code, Peer-to-Peer Communications, 1996; ISBN 1-57398-013-7
UNIX Shell Programming, Yashawant Kanetkar

[edit] External links
Wikibooks' Guide to Unix has more about this subject:
wikijuniorThe Unix Tree: files from historic releases
The Unix Guru Universe
The Unix Heritage Society
A more complete map of the different Unices and derivatives
What is UNIX, Anyway?
The Creation of the UNIX Operating System
Over 50 flavors of Unix @ Unix Guru Universe
UNIX Evolution by Ian F. Darwin and Geoffrey Collyer
Unix at the Open Directory Project
The Open Group UNIX System Homepage
Unix History
The Unix Acronym List
Unix As Literature
Unix History A large graphical family tree of Unixes
SDF Public Access UNIX System
The Unix Forums
Unix Power
A very interesting Unix tutorial by Douglas Wilhelm Harder, from the University of Waterloo
The UNIX-Haters' Handbook. An uncomplimentary anthology of early (and oft-forgotten) Unix history as revealed by web posts of early users.

LINUX

The primary difference between Linux and many other popular contemporary operating systems is that the Linux kernel and other components are free and open source software. Linux is not the only such operating system, although it is the best-known and most widely used. Some free and open source software licences are based on the principle of copyleft a kind of reciprocity: any work derived from a copyleft piece of software must also be copyleft itself. The most common free software license, the GNU GPL, is used for the Linux kernel and many of

WINDOWS 95

Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft, and was a significant progression from the company's previous Windows products. During development it was referred to as Windows 4.0 or by the internal codename Chicago.
Windows 95 was intended to integrate Microsoft's formerly separate MS-DOS and Windows products and includes an enhanced version of DOS, often referred to as MS-DOS 7.0. It features significant improvements over its predecessor, Windows 3.1, most visibly the graphical user interface (GUI) whose basic format and structure is still used in later versions such as Windows Vista. There were also large changes made to the underlying workings, including support for 255-character mixed-case long filenames and preemptively multitasked protected-mode 32-bit applications. Whereas its predecessors are optional "operating environments" requiring the MS-DOS operating system (usually available separately), Windows 95 is a consolidated operating system, which was a significant marketing change.
Contents

32-bit
Windows 95 followed Windows for Workgroups3.11 with its lack of support for older, 16-bit x86 processors, thus requiring an Intel 80386 (or compatible) processor running in protected mode.
The introduction of 32-bit File Accs in Windows for Workgroups 3.11 meant that 16-bit real mode MS-DOS is not used for managing the files while Windows is running, and the earlier introduction of the 32-bit Disk Access means that the PC BIOS isn't used for managing hard disks. This essentially reduces MS-DOS to the role of a boot loader for the protected-mode Windows kernel. DOS can be used for running old-style drivers for compatibility, but Microsoft discourages using them, as this prevents proper multitasking and impairs system stability. Control Panel allows a user to see what MS-DOS components are used by the system; optimal performance is achieved when they are all bypassed. The Windows kernel uses MS-DOS style real-mode drivers in Safe Mode, which exists to allow a user to fix problems relating to loading native, protected-mode drivers.

Long file names
32-bit File Access is necessary for the long file names feature introduced with Windows 95 through the use of the VFAT file system. It is available to both Windows programs and MS-DOS programs started from Windows (they have to be adapted slightly, since accessing long file names requires using larger s and hence different system calls). Competing DOS-compatible operating systems released before Windows 95 cannot see these names. Using older versions of DOS utilities to manipulate files means that the long names are not visible and are lost if files are moved or renamed, as well as by the copy (but not the original), if the file is copied. During a Windows 95 automatic upgrade of an older Windows 3.1 system, DOS and third-party disk utilities which can destroy long file names are identified and made unavailable (Microsoft Anti-Virus for Windows indicated that the upgrade program was itself a computer virus). When Windows 95 is started in DOS mode, e.g. for running DOS games, low-level access to disks is locked out. In case the need arises to depend on disk utilities that do not recognize long file names, such as MS-DOS 6.x's defrag utility, a program called LFNBACK for backup and restoration of long file names is provided on the CD-ROM. The program is in the \ADMIN\APPTOOLS\LFNBACK directory of the Windows 95 CD-ROM.

User interface
In the marketplace, Windows 95 was an unqualified success, and within a year or two of its release had become the most successful operating system ever produced. It also had the effect of driving other major players in the DOS-compatible operating system out of business, something which would later be used in court against Microsoft.
Internet Explorer 4.0 came with an optional shell update known as Windows Desktop Update that gave Windows 95 (and NT 4.0) a user interface and several updated shell features that would become the graphical user interfae of Windows 98. The last release of Windows 95, that is, OEM Service Release 2.5 (Version 4.00.950C) includes IE4 on the Setup CD (but not in slipstreamed form) and installs it after Windows 95's initial setup and first boot is complete.
Only the 4.x series of the browser contained the shell update, so those that wanted the new shell had to install IE4 with the desktop update before installing a newer version of Internet Explorer.
Windows 95 marked the introduction of the Start button and taskbar to Microsoft's GUI, both of which have remained fixtures of all subsequent versions of Windows, although the word "Start" was dropped from the button in Windows Vista, with the company preferring to label the button with the Windows logo ("Start" is still present as a tooltip and in the classic UI mode).





While Windows 95 was originally sold as a shrink-wrapped product, later editions were provided only to computer OEMs for installation on new PCs. The term OEM Service Release is frequently abbreviated OSR, as in OSR1 or OSR2.1. Thus, for example, OSR1 was the OEM release that was identical to Windows 95 retail with Service Pack 1 applied (with the addition of Internet Explorer). In order to maintain compatibility with existing programs, Windows 95 has an internal version number of "4.00.950", regardless of the internal build number, thus reflecting Windows 95's alternative identity as "Windows 4.0" (similarly, the original edition of Windows 98 has an internal version number of Windows 4.10.1998.) Later versions are sometimes referred to by the trailing letter appended to this version string, such as Windows 95 B for OSR2 and OSR2.1.

System Requirements
Official system requirements were an Intel 80386 DX CPU of any speed, 4 MB of system RAM, and 50 MB of hard drive space. These minimal claims were made in order to maximize the available market of Windows 3.1 converts. This configuration was distinctly suboptimal for any productive use on anything but single tasking dedicated workstations due to the heavy reliance on virtual memory. Also, in some cases, if any networking or similar components were installed the system would refuse to boot with 4 Megabytes of RAM. It was possible to run Windows 95 on a 386 SX but this led to even less acceptable performance. To achieve optimal performance, Microsoft recommends an Intel 80486 or compatible microprocessor with at least 8 MB of RAM.
Windows 95 was superseded by Windows 98 and could still be directly upgraded by both Windows 2000 and Windows Me As of December 31, 2001, Microsoft ended its support for Windows 95, making it an "obsolete" product according to the Microsoft Lifecycle Policy. Even though support for Windows 95 has ended, the software still remains in use on some home computers because of budget issues, a lack of knowledge or lack of desire to upgrade to newer editions of Windows. Another main reason is that a computer purchased around the era of Windows 95's introduction is unlikely to meet the hardware requirements of Windows XP and Vista, and some do not wish to or are not able to buy a new computer or update their existing one. In addition, some video game enthusiasts choose to use Windows 95 for their legacy system to play old DOS games, although some other versions of Windows such as Windows 98 can also be used for this purpose.
Windows 95 has been released on both floppy disks and on CD-ROM, as some computer systems at the time did not include a CD-ROM drive. The floppy disk version of Windows 95 came on 13 DMF formatted floppy disks, excluding additional software that some releases might have featured, such as Internet Explorer. Microsoft !for Windows 95 was also available on floppy disks

WINDOWS2000

Windows 2000 is a continuation of the Microsoft Windows NT line of operating systems, replacing its predecessor, Windows NT 4.0. Originally called Windows NT 5.0, then Windows NT 2000, Microsoft changed the name to Windows 2000 on October 27, 1998. It was also the first Windows version that was released without a code name, though Windows 2000 Service Pack 1 was codenamed "Asteroid" and Windows 2000 64-bit was codenamed "Janus" (not to be confused with Windows 3.1, which had the same codename). The first beta for Windows 2000 was released on September 27, 1997 and several further betas were released until Beta 3 which was released on April 29, 1999 DEC Alpha support was removed from the final build. From here, Microsoft issued three release candidates between July and November 1999, and finally released the operating system to partners on December 12, 1999The public received the full version of Windows 2000 on February 17, 2000. Three days before the launch of Windows 2000, which Microsoft advertised as "a standard in reliability", a leaked memo from Microsoft reported on by Mary Jo Foley revealed that Windows 2000 had "over 63,000 potential known defects".After Foley's article was published, Microsoft blacklisted her for a considerable time: InformationWeek summarized the release "our tests show the successor to NT 4.0 is everything we hoped it would be. Of course, it isn't perfect either."Wired News later described the results of the February launch as "lackluster". Novellcriticized Microsoft's Active Directory, the new directory service architecture to be less scalable or reliable than their own Novell Directory Services (NDS) technology.
Originally, Windows 2000 was planned to replace both Windows 98 and Windows NT 4.0. However, that was later changed. Instead, an updated version of Windows 98 called Windows 98 Second Edition was released in 1999 as a successor to Windows 98. Microsoft released Windows 2000 Datacenter Server, targeted at large-scale computing systems with support for 32 processors, on September 29, 2000.
On or shortly before February 12, 2004, "portions of the Microsoft Windows 2000 and Windows NT 4.0 source code were illegally made available on the Internet". The source of the leak remains unannounced. Microsoft issued the following statement:
“
Microsoft source code is both copyrighted and protected as a trade secret. As such, it is illegal to post it, make it available to others, download it or use it.
”
Despite the warnings, the archive containing the leaked code spread widely on the file-sharing networks. Consequentially, on February 16, 2004, an exploit "allegedly discovered by an individual studying the leaked source code" for certain versions of Microsoft Internet Explorer was reported.
Windows 2000 is a highly modular system that consists of two main layers: a user mode and a kernel mode. The user mode refers to the mode in which user programs are run. Such programs are limited in terms of what system resources they have access to, while the kernel mode has unrestricted access to the system memory and external devices. All user mode applications access system resources through the executive which runs in kernel mode.

User mode
User mode in Windows 2000 is made of subsystems capable of passing I/O requests to the appropriate kernel mode drivers by using the I/O manager. Two subsystems make up the user mode layer of Windows 2000: the environment subsystem and the integral subsystem.
The environment subsystem was designed to run applications written for many different types of operating systems. These applications, however, run at a lower priority than kernel mode processes. There are three main environment subsystems:
Win32 subsystem runs 32-bit Windows applications and also supports Virtual DOS Machines (VDMs) , which allows MS-DOS and 16-bit Windows 3.1x (Win16) applications to run on Windows.
OS/2 environment subsystem supports 16-bit character-based OS/2 applications and emulates OS/2 1.3 and 1.x, but not 32-bit or graphical OS/2 applications as used on OS/2 2.x or later.
POSIX environment subsystem supports applications that are strictly written to either the POSIX.1 standard or the related ISO/IEC standards.
The integral subsystem looks after operating system specific functions on behalf of the environment subsystem. It consists of a security subsystem (grants/denies access and handles logons) , workstation service (helps the computer gain network access) and a server service (lets the computer provide network services).

Kernel mode
Kernel modein Windows 2000 has full access to the hardware and system resources of the computer. The kernel mode stops user mode services and applications from accessing critical areas of the operating system that they should not have access to.

Each object in Windows 2000 exists in its own namespace, as illustrated by this screenshot from SysInternal's WinObj
The executive interfaces with all the user mode subsystems. It deals with I/O, object management, security and process management. It contains various components, including:
Object manager: a special executive subsystem that all other executive subsystems must pass through to gain access to Windows 2000 resources. This is essentially a resource management infrastructure service that allows Windows 2000 to be an object oriented operating system.
I/O Manager: allows devices to communicate with user-mode subsystems by translating user-mode read and write commands and passing them to device drivers.
Security Reference Monitor (SRM) : the primary authority for enforcing the security rules of the security integral subsystem.
IPC Manager: short for Inter-Process CommunicationManager, manages the communication between clients (the environment subsystem) and servers (components of the executive).
Virtual Memory Manager: manages virtual memory, allowing Windows 2000 to use the hard disk as a primary storage device (although strictly speaking it is secondary storage).
Process Manager: handles process and thread creation and termination
PnP Manager: handles Plug and Play and supports device detection and installation at boot time.
Power Manager: the power manager coordinates power events and generates power IRPs.
The display system is handled by a device driver contained in Win32k.sys. The Window Manager component of this driver is responsible for drawing windows and menus while the GDI (Graphics Device Interface) component is responsible for tasks such as drawing lines and curves rendering fonts and handling palettes. Windows 2000 also introduced alpha blending into the Graphics Device Interface which reflects in the fade effect in menus.
The Windows 2000 Hardware Abstraction Layer, or HAL, is a layer between the physical hardware of the computer and the rest of the operating system. It was designed to hide differences in hardware and therefore provide a consistent platform to run applications on. The HAL includes hardware specific code that controls I/O interfaces, interrupt controllersand multiple processors.
The hybrid kernel sits between the HAL and the executive and provides multiprocessor synchronization, thread and interrupt scheduling and dispatching, trap handling and exception dispatching. The hybrid kernel often interfaces with the process manager and is responsible for initializing device drivers at bootup that are necessary to get the operating system up and running.
A stripped down variant of the Windows