Agenda Attention

$ Overview of These PowerPoint notes are based on $ Purpose of an (OS) Chapter 1 of textbook “A Practical $ OS Guide to ” $ Characteristics of Unix OS $ OS $ Read pages 3 to 17 $ The Drive for compatibility (POSIX standards)

Definition of an Operating System (OS) History of Unix OS

An operating system is a control $ Prior to Unix, many operating systems ran program for a that performs collections or “batches” of operations one at a the following operations: time. $ This single−user “batch−processing” approach $ allocates computer resources did not take advantage of the potential $ schedules routine tasks processing power and speed of $ provides a platform to run application software for users to accomplish tasks Enter data in Process Receive files to be later Collection or information of $ provides an interface between the user & processed “Batch” of files processed data the computer Note: batch processing lacks the advantage of immediate feedback as opposed to online processing History of Unix OS History of Unix OS

$ The Unix OS was developed (based on $ The first versions of UNIX were written Multics & CTSS operating systems) by Ken in “machine−dependent” programs Thompson at the AT&T Bell Laboratories in (such as PDP−7). 1969. He wanted to create a multi−user operating system to run “space travel” game. $ approach Dennis $ Ken’s philosophy was to create an operating Ritchie (developer of language), and system with commands or “utilities” that in 1973 they compiled UNIX in C would do one thing well (i.e. UNIX). Pipes to make could be used combine commands... operating system “portable” to other computer systems.

History of Unix UNIX Features

$ The Unix OS is a multi−user OS allowing $ Ken Thompson (recently retired more than one person to directly from ) communicate with the computer. is on left, and $ Although the OS can only work on one task is at a time, a small piece of time (time slice) is in the middle. dedicated to each task or user − this is What’s his name referred to as “time−sharing”. is on the right $ Time sharing gives the illusion that the CPU is giving all the users its full attention Illustration of Time−Sharing Development of Unix OS

Unix became a popular OS among institutions such as colleges & universities User 8 User 1 through a 4−year “try before you buy” deal.

User 2 User 7 $ Efficient and inexpensive way of networking $ Promotes Internet use and −sharing User 6 User 3 $ Open system allows for source code to be shared among many − allows for better User 4 TIME User 5 coordination among programmers

Development of Unix OS Development of Unix OS

Students at University of California (in There were versions of UNIX for the Berkley) further developed the UNIX Personal Computer (PC), such as operating system and introduced the , etc., but they didn’t catch on in BSD version of Unix popularity until Linux was developed in the early 90’s. Unix

Bell Labs Berkley Software Distribution UNIX System (5) (BSD) Proprietary Free Why Has Linux Become so History of Linux Popular?

$ Linux operating system Linus decided to make Linux OS developed by source−code for open to all: programming student Linus Torvalds $ Unlike traditional Operating Systems, anyone can modify and distribute Linux OS (as long as they $ Linus wanted to distribute source code of Linux Kernel) develop Unix−like OS $ “Competition among Hackers” allows code to be just to experiment with improved and distributed often new 386 computer at $ Many users can spot bugs in the operating system the time... or application if source code is “open”

Why Has Linux Become so Popular? Concerns

Other Factors: $ Some people claim that “there are as many $ PC’s have increased processing power and there version of Linux as there are users ” has been a shift from mainframes and $ POSIX (Portable Operating System Interface to PCs. for Computer Environments) is a government $ Since Linux is a “Unix Work−alike”, this OS has a standard to ensure consistency among reputation of being a very stable platform for different UNIX and Linux versions. networking (creating at−home servers) and $ running / maintaining applications. Many versions of Linux are approaching POSIX standard. $ Agencies such as Free Software Foundation created the GNU project to provide free software. 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.