Agenda
Overview of UNIX
Purpose of an Operating System (OS) History of Unix OS Characteristics of Unix OS History of Linux OS The Drive for compatibility (POSIX standards)
Attention
These PowerPoint notes are based on Chapter 1 of textbook A Practical Guide to Linux Read pages 3 to 17
Definition of an Operating System (OS)
An operating system is a control program for a computer that performs the following operations:
allocates computer resources schedules routine tasks provides a platform to run application software for users to accomplish tasks provides an interface between the user & the computer
History of Unix OS
Prior to Unix, many operating systems ran collections or batches of operations one at a time. This single−user batch−processing approach did not take advantage of the potential processing power and speed of computers Enter data in files to be later processed Process Collection or Batch of files Receive information of processed data
Note: batch processing lacks the advantage of immediate feedback as opposed to online processing
History of Unix OS
The Unix OS was developed (based on Multics & CTSS operating systems) by Ken Thompson at the AT&T Bell Laboratories in 1969. He wanted to create a multi−user operating system to run space travel game. Ken s philosophy was to create an operating system with commands or utilities that would do one thing well (i.e. UNIX). Pipes could be used combine commands...
History of Unix OS
The first versions of UNIX were written in machine−dependent programs (such as PDP−7). Ken Thompson approach Dennis Ritchie (developer of C language), and in 1973 they compiled UNIX in C programming language to make operating system portable to other computer systems.
History of Unix
Ken Thompson (recently retired from Bell Labs) is on left, and Dennis Ritchie is in the middle. What s his name is on the right
UNIX Features
The Unix OS is a multi−user OS allowing more than one person to directly communicate with the computer. Although the OS can only work on one task at a time, a small piece of time (time slice) is dedicated to each task or user − this is referred to as time−sharing . Time sharing gives the illusion that the CPU is giving all the users its full attention
Illustration of Time−Sharing
User 8 User 7 User 6 User 5 User 1 User 2 User 3 User 4
Development of Unix OS
Unix became a popular OS among institutions such as colleges & universities through a 4−year try before you buy deal.
Efficient and inexpensive way of networking Promotes Internet use and file−sharing Open system allows for source code to be shared among many programmers − allows for better coordination among programmers
TIME
Development of Unix OS
Students at University of California (in Berkley) further developed the UNIX operating system and introduced the BSD version of Unix
Unix Bell Labs UNIX System V (5) Proprietary Berkley Software Distribution (BSD) Free
Development of Unix OS
There were versions of UNIX for the Personal Computer (PC), such as XENIX, etc., but they didn t catch on in popularity until Linux was developed in the early 90 s.
History of Linux
Linux operating system developed by programming student Linus Torvalds Linus wanted to develop Unix−like OS just to experiment with new 386 computer at the time...
Why Has Linux Become so Popular?
Linus decided to make Linux OS source−code for Linux Kernel open to all:
Unlike traditional Operating Systems, anyone can modify and distribute Linux OS (as long as they distribute source code of Linux Kernel) Competition among Hackers allows code to be improved and distributed often Many users can spot bugs in the operating system or application if source code is open
Why Has Linux Become so Popular?
Other Factors:
PC s have increased processing power and there has been a shift from mainframes and minicomputers to PCs. Since Linux is a Unix Work−alike , this OS has a reputation of being a very stable platform for networking (creating at−home servers) and running / maintaining applications. Agencies such as Free Software Foundation created the GNU project to provide free software.
Concerns
Some people claim that there are as many version of Linux as there are users POSIX (Portable Operating System Interface for Computer Environments) is a government standard to ensure consistency among different UNIX and Linux versions. Many versions of Linux are approaching POSIX standard.
Concerns
Freedom of allowing Linux users to create servers connected up to Internet can lead to attacks from experienced hackers. Linux commands may be considered user− unfriendly although GUIs are now used. Prior reputation for difficult install process including the loss of data on other hard disk partitions.