The Unix Operating System

1
The Unix Operating System

• Chapter 1

2
History of Unix

• Developed at ATT Bell Laboratories
• First major improvement over the single job/batch
  mode system
• New features added by Unix
• Multi-user
• Interactive
• Enabled sharing of data and programs
• Extended by the Computer Systems Research Group
  at UC Berkeley resulting in the Berkeley Software
  Distribution (BSD) version of UNIX

3
UNIX and Hardware Manufacturers

• Why UNIX is popular with hardware manufacturers
• portable
• Takes advantage of the available hardware power
• Eliminated the need for HW manufacturers to
  develop costly, proprietary operating systems

4
UNIX and Software Manufacturers

• Why UNIX is popular with software manufacturers
• Provides an ideal software development
  environment
• Eliminated the need to make multiple versions of
  a software to run on proprietary operating systems

5
The UNIX Standard

• Hardware manufacturers adopted and modified UNIX
• Made the OS less standard
• Made it difficult for SW developers to create a
  product that will run on all version of the UNIX
  system
• ATT melded their version of UNIX with all the
  other popular upgrades by various groups such as
  BSD and established a written standard, System 5
  Interface Definition.
• Standard later evolved to POSIX

6
Why is UNIX Portable?

• It is written in a machine-independent language,
  C
• C was actually developed so that UNIX can be made
  machine-independent. UNIX was initially written
  assembly language that is machine dependent

7
UNIX Feature Overview (1)

• Utilities
• Also known as commands
• Utility programs universally required by users
  such as sort, list files and directories
• Multi-user
• Multi-tasking
• System kernel
• True OS
• Controls computer resources and schedule jobs
• Has system calls programs can use to interact
  with the kernel

8
UNIX Feature Overview (2)

• File structure
• Supports tree-like organization for files and
  directory
• Provides a link feature access files by 2 or
  more different names
• File Security
• Protect users data from other users
• Shell
• Interface between user and the operating system
• Bourne, C and Korn shells

9
UNIX Feature Overview (3)

• Shell functions
• May be used as a programming language
• Basic shell allows for simple, interpreted
  programming
• Bourne and Korn shells allows for memory-stored
  and compiled programs
• C shell provides for aliasing but not basic shell
  functions
• Alias allows user to define new commands and
  to make standard feature perform in non-standard
  way.
• Korn shell provides both shell functions and
  aliasing

10
UNIX Feature Overview (4)

• Filename generation
• Allows for use of wildcards () in retrieving
  filenames
• Device independent I/O
• I/O are device independent. They can be
  redirected to and from any appropriate device.
• Example, the same commands can
• Output to any output device or file
• Received input the terminal or disk file

11
UNIX Feature Overview (5)

• Interprocess communication
• Pipes send the output of one program as input
  to another program
• Filter process a stream of input data to yield
  a stream of output data
• Job control
• Allow users to work on several jobs at once,
  moving one or another to the background or
  foreground
• E-mail
• Screen-oriented editor
• vi, text editor

12
UNIX Feature Overview (6)

• File scrolling
• more utility display information one screen at
  a time
• Networking utilities
• Give users access to remote systems over a
  variety of networks.