1. Agenda UNX122_022_w1_p3 Overview of UNIX
Purpose of an Operating System (OS)
History Unix OS
Characteristics of Unix OS
History of Linux OS
The Drive for compatability (POSIX standards) 2

2. Attention
These PowerPoint notes are based on Chapter 1 of textbook “A Practical Guide to Linux”
Read pages 3 to 17 6

3. 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 7

4. 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 8

5. 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 He wanted to create an 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... 9

6. History of Unix OS
The first versions of UNIX were written in “machine-dependent” program (such as PDP-7).
Ken Thompson approach Dennis Ritchie developer of C program), and in 1973 they compiled UNIX in C programming language to make operating system “portable” to other computers systems. 10

7. 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… 11

8. UNIX Features
The Unix OS is a multi-user OS allowing more that more 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 12

9. Illustration of Time-Sharing
User 8
User 1
User 2
User 7
User 6
User 3
TIME
User 4
User 5 13

10. 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 14

11. Development of Unix OS
Students at University of California (in Berkley) further developed the UNIX operating system and introduced the BDS version of Unix
Unix
Bell Labs UNIX System V (5) Proprietary
Berkley Software Distribution (BSD) Free 15

12. 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. 16

13. 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... 17

14. Why Has Linux Become so Popular?
Linus decided to make Linux OS source-code for Linux Kernal 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” allow code to be improved and distributed often
Many users can spot bugs in the operating system or application if source code is “open” 18

15. Why Has Linux Become so Popular?
Other Factors:
PC’s have increased processing power and a there has been a noted shift from mainframes and minicomputers to PCs.
Since Linux is a “Unix Work-alike”, this OS has a reputation to be a very stable platform for networking (creating at-home servers) and running / maintaining applications.
Agencies such as Free Software Foundation created GNU project to provide free software. 19

16. 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. 20

17. 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. 21