1. 1 A Brief History of the Development of Operating Systems and Some Fundamental Concepts Ass. Prof. Emin Korkut

2. 2 OPERATING SYSTEM Operating System is the most important program which runs on a computer. An operating system is a main program to be run on a general purpose machine that none of the other programs can be run without running this main program. An operating system is necessary to run a general purpose computer. recognizes the data entered through the keyboard sends output to the display screen also keeps track of files on the disk and recognizes the type of the file. controls the peripheral devices like disk drives, printers, scanners.

3. 3 If the computer system is large then the responsibilities of the operating system increases. In this case the system is designed at multitasking and multiuser or even multithread level. the operating system guarantees that different programs and users running at the same time do not interfere with each other. The security of the system is controlled by the operating system such that it ensures the inaccessibility of the unauthorized users to the system.

4. 4 The operating systems can have some of the following features: Multiuser: This feature makes it possible to allow two or more users to run programs at the same time. The number of the users which can run programs at the same time depends on the operating system. Multitasking: If a user wants to run more than one programs at the same time, the operating systems facilitating this possibility are called Multitasking Operating Systems. Multithreading: This feature enables the operating system to run the different parts of a single program at the same time. This may reduce the execution time drastically and is important for the system optimization.

5. 5 Multiprocessing: This feature enables the operating system to control more than one CPU computers. If a computer has more than one CPU then the organization of data transfer and data processing becomes more complicated and necessitates some extra capabilities in the operating system. This capability is multithreading.The operating system can create more than one threads and organizes their utilization in the CPUs. To be more understandable it is better to give the meaning of thread. It is a part of the program that it can be run independently from the other part of the same program. Real-time: Not available for general purpose operating systems like DOS and UNIX. Every input to the system operated by this type of operating systems takes an instant response from the operating system. This feature is found in the specific purpose systems whose tasks and responsibilities are limited to a very specific aim.

6. 6 A software platform (operating system) is used to run other programs. These programs are called application programs. Softwares can be collected under two general groups: 1. System Softwares 2. Application Softwares. The system software is written in assembly languages or low level languages. These are like operating systems, compilers and so on. Whereas application softwares are created by using system software. Application software are frequently called applications.

7. 7 DOS is an operating system Microsoft WORD is an application program. An application program designed for a specific operating system can run only under that operating system. The operating systems are mostly considered as platforms or software platforms and the application programs are platform dependent unless they have a version for each one of the existing platforms. Mostly the application programs are distributed in binary form although there is an increasing tendency to make the source codes freely available.

8. 8 The most widely used operating systems for personal computers are: DOS OS/2 Windows MacOS FreeBSD SCO Linux. Command line interpreter: The interaction between the user and operating system is provided by a software; this is called command line interpreter. For example, the entering of ls command of Linux or dir command of DOS are examples to this end.

9. 9 Shell: Its is a sophisticated software which provides a programmable bundle of commands usually used for powerful operating systems. Shell programming is frequently called scripting. The command line interpreter or command processor is used in non-graphical interfaces. If the interface between the user and operating system is graphical like X Windows of Linux or Windows of Microsoft then mouse can be used as a data entering device.

10. 10 BIOS BIOS stands for Basic Input Output System. It is a built-in software and performs whatever it can do without accessing programs from a disk. Actually it determines what a computer can do without accessing a disk. For personal computers BIOS contains all the code required for the controlling the keyboard, display screen, disk drives, serial communications and so on. It is located into a ROM chip which is frequently called ROM BIOS. This structure guarantees that the BIOS will always be available without being affected by the disk crashes. enables the computer to boot itself.

11. 11 Mainframe Old days of computer systems development of IBM machines. The systems have a main unit including the CPU(s), RAM, hard disk(s) and some other internal and peripheral devices for handling many tasks connected to some central location many terminals connected to this central structure. There was no today's keyboard directly connected to the central unit of the system. There were keyboards but connected to the card punchers. The commands to be executed could be written on just a single card which can keep only a line including at most 80 characters. If the data or command can not be totally inserted into a single card you ought to use a second card for continuation.

12. 12 When you press one of the keys on the keyboard of the card puncher some holes were punched on the card. The locations of the holes in the columns of the card were to be used to determine the numerical counterpart of the keystroke at the level of binary number representation. In order to write a program consisting of, for example, 1000 lines you ought to punch 1000 separate cards and to submit these cards for execution you had to go to the center of the system by carrying the cards in a box. Imagine that you designed a software which has millions of lines like the today's applications do.

13. 13 The utilization of the monitors and the keyboards which are connected to the central unit of the mainframe was a real revolution. Today, there are still main frames but most widely used structures are either personal computers or workstations. At the early years of the computer age there were no internet or a similar backbone for the networking. Hence the network security was not a problem. The mainframes are frequently called big iron. IBM mainframes was often called big blue. The most famous operating system on the IBM mainframes is VM which is an acronym for the statement Virtual Machine. The predecessors of VM were VS1, VS2 and DOS which is an acronym for the statement Disk Operating System. Do not confuse this DOS with the DOS for personal computers.

14. 14 UNIX UNIX stands for Uniplexed Information and Computing System. generally a non--real--time operating system. popular because it is available for many different hardware platforms. very well documented so one can learn a lot of points about it from the operating system itself. There are so many source code available for it. also popular because it is widely used at universities and institutions for scientific research. The initial development of UNIX was made by Ken Thompson and Dennis M. Ritchie in 1969. The first version of UNIX was completed two years later.

15. 15 It was written in Assembly Language so somehow machine dependent. The documentation manual was called Edition 1. The system itself was also called Edition 1 frequently. At the beginning it was used for text processing in the preparation of the patents. Later, especially in the mid--life of UNIX there had been a lot of important steps and the operating system was redesigned. The assembler or computer architecture dependence of UNIX ought to be removed for the creation of platform independent operating system. This implied that the operating system should have been written by a platform or assembler independent programming language.

16. 16 Kernighan and Ritchie worked together to create a new low level programming language which would be very close to the machine language and also portable, that is, independent from the hardware platform. They created language which was called A. A was insufficient because of the lack of many important features expected for platform independence and also for closeness to assembler. The efforts continued and the next step was B language which was still insufficient for the ultimate goal and was soon left. The final software obtained after these studies was called C. After the born of C UNIX was rewritten by using C instead of assembler. This gave very competitive properties to UNIX and made it very famous. It was soon started to be used at universities.

17. 17 The UNIX systems are most preferred, reliable and dominant operating systems in academic institutions. The System V was an AT&T UNIX System which was first released in 1983. It supported many types of interprocess communication. The other releases of System V followed this very first version with increasing version numbers. The latest version of System V has the version number 4.2 and contains an ANSI C compiler. Another UNIX development was accomplished by the Computer SystemsResearch Group at the University of California at Berkeley. At the beginning these were a bundle of new utilities for the System V version of UNIX and grew to be an entire operating system. The operating system constructed in this way called BSD which is an acronym for the statement Berkeley Source Distribution. It ran on a DEC VAX minicomputer.

18. 18 DOS DOS stands for Disk Operating System and it can be in fact any operating system. However the tendency of the people is to refer MSDOS which is an acronym for of Microsoft Disk Operating System. MSDOS was developed for the IBM compatible personal computers. The initial version of DOS was very simple. It has been improved. This does not mean that DOS approached into a powerful state of UNIX. 16--bit operating system. does not support multitasking and multiple users.

19. 19 Due to insufficiency of MSDOS, new operating systems was developed, that is, the WindowsX.Y series where X takes at most the value of 3. These operating systems were relying on DOS for many services. By the born of Windows95 this philosophy was changed and the new operating systems to be constructed were designed without relying on DOS although a facility of executing DOS based programs have been available. As the the market share of these systems increases DOS is expected to be unnecessary and be discarded. This does not mean the death of DOS. As a matter of fact, Caldera, Inc. developes and markets a DOS version which is called DR--OpenDOS. It is freely distributed.

20. 20 Microsoft Windows According to some estimates the 80 percent of the all personal computers is run by Windows. The remaining percentage is divided amongst MacOS, Linux and some other ones. Windows provides a GUI which is an acronym for the statement Graphical User Interface. supports virtual memory management, multitasking and support for many peripheral devices. However, except Windows NT and Windows 2000, it does not support multiple users. Even for NT and 2000 the support for multiple users is not strong as much as UNIX.

21. 21 The first widely used versions of Windows were the releases whose versions denoted as Windows3.x at the end. 16--bit operating systems and had a lot of limitations and now almost disappeared. Windows 95 Released in 1995. It shows a significant advance over Windows 3.1. The most important advance is its 32--bit structure which makes the operating system faster. However applications must be written specifically for this system. It has removed DOS as the underlying platform although it can run older applications which can run on the older versions of the Microsoft Windows. This means the removal of 640KB main memory and 8 character filename limitations.

22. 22 Windows 98 Released in 1998. Its original name was Memphis and later Windows97. the basic structure of this operating system is almost same as Windows95. Windows NT Windows NT stands for Windows New Technology. The most advanced operating system of Microsoft. It can support a lot of facilities presented by UNIX systems networking power and reliability are less than UNIX. Two types of NT system are available. These are called server and workstation. Server is needed when a network structure will be created whereas workstation works just as single entity, just for a single user client.

23. 23 Windows2000 This has been developed instead of the newest version of Windows NT. It seems to have a lot of bugs although its capabilities have been increased.

24. 24 Linux New system like UNIX for personal computers has been seek due to the dominance of the Microsoft products over the area of personal computers, In 1991, Linus Torvald of Helsinki University in Finland attempted to write a kernel working for Intel processors of those days and the kernel was opened to the public domain with a demand for support to improve it and also develop application programs through Internet. The response of the people on the Internet was very positive and thousands of the computer wizards concerned with this attempt and gave a hand.

25. 25 This was the born a new operating system which was called Linux later. At the beginning it was weak and very limited. But after 9 years passing with an incredible improvement it became most powerful operating system of the personal computer area. Now it is second in the servers all over the world ahead Microsoft products and threatens Microsoft products in individual systems with a very rapidly increasing percentage. More and detailed information about this operating system is going to be given later in the third chapter. Multiple user at the topmost level, the capability of multithreading, multitasking with the best optimization are available.

26. 26 VIRUS free of course and it is very stable, that is, it can run without any problem by years. Kernel and Shell Kernel is the core or heart of the operating system. It activates a medium in which all application programs can run. It activates the sockets to the peripheral devices and takes care of memory management. However, the run of the application programs are provided by the execution environment created by a sub software which is called Shell. There are a lot of shells for Linux. Amongst these, perhaps the most widely used one is BASH which is an acronym Bourne Again Shell. csh, tcsh, ksh, pdksh, zsh are other important shells used by the Unix community.

27. 27 VIRUS VIRUS is not a biological entity (at least now ) which infects your operating system and destroys its functionality. It stands for Vital Information Resources Under Siege so there must be a siege possibility for the operating system. The worst aspect of the virus is its capability of copying itself. The operating system are sometimes classified into two categories as open and close systems. Modular systems which can do multitasking, multithreading and managing multiple user level utilization are almost entirely open systems. For example UNIX and Linux are open systems while DOS and old Windows3.1 are closed systems.

28. 28 Open systems can be considered almost virus free although there is a possibility of writing a program which makes the system collapsed. However the design of such software is hard as much as creating a new operating system and even if it is created the loading of its entire structure into the system to be affected is a matter of hacking since the existence of root level users and the inaccessibility of root users in sufficiently secure systems.

29. 29 X Window X Window is the GUI for UNIX systems. It was developed quite before than the Microsoft Windows systems which are in fact based on the same philosophy used by X Windows. Today, there are desktop environments like KDE and Gnome which are set of utilities working on a X window medium. X Windows operates in according to the client --server model. It is a free software.