About GNU

Like Linux, GNU (pronounced guh-noo) is also a free software operating system. Its name is a recursive acronym for “GNU’s not Unix” which was chosen because while it is Unix based, it is freeware and contains no Unix code. As of 2007, GNU is being actively developed although a complete system has not yet been released.

The gentleman responsible for developing GNU is Richard Stallman, a former employee at MIT. He believed computer users should be free, as most were in the 1960s and 1970s; free to study the source code of the software they use, free to share the software with other people, free to modify the behavior of the software, and free to publish their modified versions of the software. This philosophy was published in March 1985 as the GNU Manifesto.

Much of the needed software had to be written from scratch, but existing compatible free software components were used. Most of
GNU has been written by volunteers; some in their spare time, some paid by companies, educational institutions, and other non-profit
organizations.

In 1992, the operating system was more or less finished except for the kernel. The GNU project had a microkernel, and to add the necessary Unix-kernel-like functionality to their microkernel, they were developing a project called “Hurd”. However, “Hurd” was still very incomplete.

That year, Linus Torvalds released his Unix-like kernel Linux as free software. The combination of the Linux kernel and the GNU system made for a whole, Unix-like free software operating system. Linux-based variants of the GNU system became the most common way in which people use GNU.

As of 2005, Hurd is in slow development, and is now the official kernel of the GNU system.

About Linux

The first Linux systems were completed in 1992 by combining system utilities and libraries from the GNU project which is another operating system we’ll address next.


Predominantly known for its use in servers, Linux is used as an operating system for a wider variety of computer hardware than any other operating system including desktop computers, super computers, mainframes, and embedded devices such as cell phones. Linux is packaged for different uses in Linux distributions which contain the kernel along with a variety of other software packaged tailored to its intended use.


Linux alleges that people regard the system as suitable mostly for computer experts because mainstream computer magazine reports cannot explain what Linux is in a meaningful way as they lack real-life experience using it. Furthermore, the frictional cost of switching operating systems and lack of support for certain hardware and application programs designed for Microsoft Windows have been two factors that have inhibited adoption.


However, as of early 2007, significant progress in hardware compatibility has been made, and it is becoming increasingly common for hardware to work “out of the box” with many Linux distributions. Proponents and analysts attribute the relative success of Linux to its security, reliability, low cost, and freedom from vendor lock-in.


The primary difference between Linux and other contemporary operating systems is that the Linux kernel and other components are open source software. That means that users have permission to study, change, and improve the software. They can then redistribute it in modified or unmodified form. This is usually done in a public and collaborative manner.


Linux is not the only such operating system, although it is the most well-known and widely used one. Some open source licenses are based on the principle of “copy left”, a kind of reciprocity: any work derived from a copy left piece of software must also be copy left itself. One of the advantages of open source is that it allows for rapid software bug detection and elimination which is important for correcting security exploits.


Another advantage of Linux as an operating system is inter- operability. That means, it can run software from other companies such as Mac and Windows. This makes it hugely advantageous to the open market as inter-operability in an operating system is rather uncommon as of late.


People have actually taken on the promotion of Linux in what might be considered almost a cult-like following. In many cities and regions, local associations known as Linux Users Groups.


Many Windows applications can be run on the Linux operating system. While there are not many games or applications that are available with Linux, there are still others that can run easily on the software.

About UNIX

The UNIX operating system was developed in the 60’s and 70’s by a group of AT & T employees at Bell Labs. Unix is used by both servers and workstations and is the basis for a wide variety of other operating systems.

The UNIX system was designed to be portable, multi-tasking and multi-user in a time-sharing configuration. There are various concepts that are unique to all UNIX systems. These concepts include:

The use of plain text for storing data

A hierarchical file system

Treating devices and certain types of inter-process communication as files

The use of a large number of small programs that can be strung together through a command line interpreter using “pipes” as opposed to a single monolithic program with the same functionality.

The operating system under UNIX consists of many of the utilities listed above along with the master control program which is called the “kernel”. The kernel helps start and stop programs, handle the file system, take care of other common high level tasks that most programs share and schedule access to hardware to avoid conflicts if two programs try to access the same resource or device simultaneously.

Besides the main kernel, UNIX systems also had micro-kernels which 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 where a “normal” computer consisted of a hard disk for storage and a data terminal for input and output, the UNIX file model worked quite well as most input/output 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 1980’s led to facilities for non-blocking input/output forms of inter-process communications other than just pipes, as well as moving functionality such as network protocols out of the kernel.

Just as with other operating systems, the programming was updated periodically to add other features and to streamline processes that the system would run. Ironically, the importance of the UNIX system is quite far-reaching. In fact, some experts call it the most important system you’ll never use.

UNIX is mostly used by Internet servers and database servers. It is a very efficient multi-user, multi-tasking operating system traditionally used by large companies and educational institutions.

It is scalable from a small system right up to a mainframe-class system (all you need to do is add extra hardware), which makes it suitable for anyone looking for a low cost, reliable operating system.

For programmers it has a wonderful set of built-in utilities, a programmable shell (command/user interface) and a straight forward structure that makes it very easy to quickly produce quite complex programs. For end users, UNIX has a friendly graphical interface (called X Windows) and many business applications and games.

As we said, UNIX is used as a basis for other operating systems. One of those is Linux.

Brief Description About MAC OS

Apple was very strong in advertising this new machine. After it was created, they actually bought out all thirty-nine pages of advertisement space in Newsweek Magazine’s November/December,
1984 edition. It worked incredibly well and the investment paid off as


Macs began flying off the shelves.




The first version of Mac OS along with subsequent updates were different from other operating systems in that this OS didn’t use command line interface but rather user friendly interface. Many people think that Windows was the first to employ GUI, but Mac had them beat.


Updates to the OS mostly focused on changes to the “finder” which is an application for file management which also displays the desktop. Prior to version 5, the finder could only run one application at a time. When version 5 was released, it contained multi-finder which could run several applications at once.


Time was given to background applications only when the foreground running applications gave it up in co-operative multitasking, but in fact most of them did via a clever change in the operating system’s event handling.


System 5 also brought Color Quick Draw to the Mac II. This significantly altered the extent and design of the underlying graphics architecture but it is a credit to Apple that most users, and perhaps more importantly existing code, were largely unaware of this.


System Software 5 was also the first MAC operating system to be given a unified system software version number as opposed to the numbers used for the system and finder files.


In 1991, System 7 was released. It was the second major upgrade to the Mac OS adding a significant user interface overhaul, new applications, stability improvement, and many new features.


The most visible change was a new full-color user interface. Although this feature made for a visually appealing interface, it was optional. On machines not capable of displaying color or those with their display preferences set to monochrome, the interface defaulted back to the black and white of previous versions. Only some interface elements were colorized: scrollbars had a new look but push buttons remained in black and white.


The biggest feature added in system 7 included the built-in co- operative multitasking. In system 6, this function was optional through the multi finder. System 7 also introduced aliases which are similar to shortcuts that were introduced in later versions of Windows.


System extensions were enhanced by being moved to their own subfolder. A subfolder in the system folder was also created for the control panels. A smaller update – dubbed system 7.5 – included the extensions manager, a previously third party program which simplified the process of enabling and disabling extensions.


System 7 moved the Mac to true 32-bit memory addressing necessary for the every-increasing amounts of RAM available. Earlier systems used the lower 24 bits for addressing and the upper 8 bits for flags. This was an effective solution for earlier Mac models with very limited amounts of RAM, but it became a liability later. Virtual memory support was also added as a separate, optional feature.


The Apple menu, home only to desk accessories in system 6 was made more general purpose: the user could now make often-used folders and applications – or anything else they desired – appear in the menu by placing aliases to them in an “Apple Menu Items” subfolder of the system folder.


The trash folder, under system 6 and earlier, would empty itself automatically when shutting down the computer or, if multi-finder were not running, when launching an application. System 7 re- implemented the trash as a special hidden folder allowing files to
remain in it across reboots until the user deliberately chose the “Empty


Trash” command.




There were some other “high level” additions in system 7. Many people felt that Apple dropped the ball on some of these additions and accused the company of not fully thinking through these updates. Microsoft was accused of the same thing with earlier versions of Windows as well.


One of the most confusing aspects of the Mac OS was the reliance on countless System Enablers to support new hardware which would prove to plague the Mac OS all the way to version 8 after which iMac introduced its “New World” architecture. Although the iMac itself requires a system enabler with OS 8 as other Macs released at that time, Macs released after the iMac do not require a system enabler.




Another problem encountered was that various system update extensions with inconsistent version numbering schemes. Overall stability and performance of the Mac OS gradually worsened during this time which introduced Power PC support and 68K emulation.


When version OS 7.6 was released, the stability of the operating system was much better. People began to fully embrace the Mac OS and their legitimacy returned as a popular operating system.


System 7 also saw the introduction of an interactive help application, and the addition of “Stickies” which were basically virtual Post-It notes. Many Mac users still have OS 7 on their Apples.


Two other versions would follow in OS 8 and OS 9 each improving on the previous version. Apple continued to develop updates to their operating system making it more stable and capable of more tasks working efficiently to bring Mac into the 21st century.


The most recent version and one that is used on new systems today is Mac OS X. This version provides a stable operating environment for the Mac PC and offers more flexibility than other systems. The graphics are updated with lots of color and a flashier look.

Basic Knowledge About MAC OS

In 1984, Apple Computer introduced the Apple Macintosh personal computer. The first version was the Macintosh 128K model which came bundled with the Mac OS operating system then known as the “System Software”. The Mac is often credited with popularizing
the graphical user interface (GUI).


The Mac OS has been pre-installed on almost every Macintosh computer ever sold. The operating system is also sold separately from the computer just as with Microsoft Windows. The original Mac OS
was heavily based on the Lisa OS previously released by Apple for the Lisa computer in 1983. It also used concepts from other operating systems previewed by Apple executives.

In 1984, Apple partnered with Microsoft in an agreement that would have Microsoft creating versions of Word and Excel for the Mac OS. For the majority of the 1980’s, the Mac OS lacked a large amount of compatible software, however, the introduction of System 7 saw more software becoming available for the platform.

System 6 was the first major revision of the operating system, although the Mac OS kernel was kept the same from the System 7 revision until Mac OS 9.

The Macintosh project started in early 1979 with Jeff Raskin who envisioned an easy-to-use low-cost computer for the average consumer. In September of ’79, Raskin was given permission to start hiring for the project.

In January of 1981, Steve Jobs completely took over the Macintosh project. Jobs and a number of Apple engineers visited Xerox PARC in December of 1979 which was three months after the Lisa and Macintosh project had begun.

After hearing about the pioneering GUI technology being developed at Xerox PARC from former employees like Raskin, Jobs negotiated a visit to see the Xerox Alto computer and Smalltalk development tools in exchange for stock options. This was probably one of the best business moves Jobs had ever made.

The final Lisa and Macintosh operating systems used concepts from the Xerox Alto, but many elements of the GUI were creating by Apple including a menu bar and pop-up menus. Specifically, the click and drag concept was developed by Jeff Raskin.

Unlike the IBM PC which used 8 KB of system ROM for power-on self test and basic input/output chores, the Mac ROM was significantly larger at 64 KB and held key OS code. Andy Hertzfeld was responsible for most of the original coding. He was able to conserve some of the ROM space by interweaving some of the assembly language code.

In addition to coding the ROM, he also coded the kernel, the Macintosh Toolbox, and some of the desktop accessories as well. The icons of the operating system which represented folders and application software were designed by Susan Kare who later designed the icons for Microsoft Windows 3.0.