UNIX is MULTICS OS, i.e Multi user OS., Invented by Ken Thompson and Dennis Richie at AT & T Bell telephone Elaborateness USA in the year 1972., Till there there is only one OS is the market ., i.e DOS.
The first version of UNIX was written in Machine Language., Afterwords it was rewritten in Assembly Language., later it moves into B language(BCPL)., after the invention of C Language by Thompson and Richie UNIX OS was rewritten in C Language., presently available.
Basic Feature of UNIX OS.
- Unix is more flexible and can be installed on many different types of machines, including main-frame computers, supercomputers and micro-computers.
- Unix is more stable and does not go down as often as Windows does, therefore requires less administration and maintenance.
- Unix has greater built-in security and permissions features than Windows.
- Unix possesses much greater processing power than Windows.
- Unix is the leader in serving the Web. About 90% of the Internet relies on Unix operating systems running Apache, the world's most widely used Web server.
- Software upgrades from Microsoft often require the user to purchase new or more hardware or prerequisite software. That is not the case with Unix.
- It is a Multics user OS.
- It is a Multitasking OS.
- It provide primitives that build complex structures from smaller ones.
- It provide more security to user programs.
- It support different types of users.
- It support hierarchical file system.
Unix has
a layered structure.
1. Innermost layer is the hardware—CPU,
memory, devices.
2. The core components of OS is
referred as the kernel(a central or essential part) in Unix. The kernel, interacts
directly with the hardware and provides the services to the user programs.
These user programs don't need to know anything about the hardware.
3. Unix Shells: A shell
acts as an interpreter between a user and the kernel. A user interacts with the
kernel through a set of standard system calls(aka Unix commands or
shell commands).
Unix is
a multi-user, multi-tasking operating system. Many users can
log on simultaneously, each running many programs. It is the kernel’s job to
keep each process and user separate and to control accesses to system hardware
including CPU, memory, disk, and other I/O devices.
Important Features:
Over 40 years of experience
· Available for almost any hardware
platform
· Robust: made to keep on running
· Secure and versatile
· Scalable
Many different dialects
· Many proprietary systems: bundling
and system specific implementation of commands/packages
· Not user friendly, confusing for
beginners
· Proprietary hardware is expensive
The kernel
The kernel
is the core of the UNIX operating system. Basically, the kernel is a large
program with many modules that is loaded into memory when the machine is turned
on, and it controls the allocation of hardware resources. The kernel knows what
hardware resources are available (like the processor(s), the on-board memory,
the disk drives, network interfaces, etc.), and it has the necessary
programs(drivers) to talk to all the devices connected to it.
The
standard utility programs
These
programs include many programs ranging from simple utilities like cp, which
copies files, to complex utilities, like the shell programs that allow you to
issue a series of commands to the operating system.
The system
configuration files
The system
configuration files are read(used) by the kernel, and some of the standard
utilities. Certain aspects of kernel and utilities can be controlled by
changing the standard configuration files. In other words, they can be
customized.
One
example of a system configuration file is the filesystem table
"fstab" , which tells the kernel where to find all the files on the
disk drives. Another example is the system log configuration file
"syslog.conf", which tells the kernel how to record the various kinds
of events and errors it may encounter.
Login: One thing to remember is Unix
is case sensitive—including login name & password
· Logout: Type either “^D”
or “exit”
· Leave a shell: If you have changed a shell,
to go back to a previous shell, type “exit”.
· Identity: A user is identified by uid(user
id) + gid(group id)—type id to see your
id—group id is used by administrator to assign access rights—typegroups to
see all the groups you belong to.
Types of Users in Unix OS.
1. Root User or System Administrator
2. Ordinary User or Individual User
3. Group user or User Group
All the above users login in from any
terminal whether it is server or client.
Standard
System Prompts to above Users.
1. Root User or System Administrator is # prompt.
2. Ordinary User or Individual User is $ prompt.
3. Group user or User Group $ prompt.
How to write a C Program on UNIX OS.
$ vi file name (file name.c if it is a C Language Program)
vi editor opens is Esc mode or Command mode., Press i changes Insert mode.
Type the C Language program.
for saving
press Esc key :wq
for compilation $ cc file name
shows error list or successful compilation.
if errors occur go to $ vi file name
if program is compiled successfully for running
$ a.out
C Language Program result will be displayed.
i.e Compilation of C Language Programs on UNIX OS.
