WHAT IS UNIX AND DIFFERENT FEATURES OF UNIX

 1.UNIX IS A CUI OPERATING SYSTEM.OPERATING SYSTEM IS AN INTERFACE BETWEEN HARDWARE AND APPLICATIONS SOFTWARE'S.IT SERVES AS THE OPERATING SYSTEM FOR ALL TYPES OF COMPUTERS,INCLUDING SINGLE-USER PERSONAL COMPUTERS AND ENGINEERING WORKSTSTIONS,MULTI-USER MICROCOMPUTERS,MINI COMPUTERS,MAINFRAMES,AND SUPER COMPUTERS ,AS WELL AS SPECIAL -PURPOSE DEVICES THE NUMBER OF COMPUTERS RUNNING A VARIANT OF UNIX HAS GROWN EXPLOSIVELY,WITH APPROXIMATELY 20 MILLION COMPUTERS NOW RUNNING UNIX AND MORE THAN 100 MILLION PEOPLE USING THESE SYSTEMS.THE SUCCESS OF UNIX IS DUE TO MANY FACTORS,INCLUDING ITS PORTABILITY TO A WIDE RANGE OF MACHINES,ITS ADAPTABILITY AND SIMPLICITY,THE WIDE RANGE OF TASKS THAT IT CAN PERFORM,ITS MULTI-USER AND MULTITASKING NATURE,AND ITS SUITABILITY FOR NETWORKING,WHICH HAS BECOME INCREASINGLY IMPORTANT AS THE INTERNET HAS BLOSSOOMED.

HISTORY OF UNIX:

BEFORE DEVELOPMENT OF UNIX OPERATING SYSTEM at AT AND T BELL LABS,SOFTWARE TEAM LEAD BY KEN THOMSON,DENNIS RITCHIE AND RUDD CANDAY WORKED ON MULTICS PROJECT .MULTICS STAND FOR MULTI INFORMATION COMPUTING SYSTEM.THE AIM OF THIS PROJECT IS TO SHARE THE SAME DATA BY 'N' NUMBER OF USER AT THE SAME TIME.INITIALLY,MULTICS WAS DEVELOPED FOR ONLY TWO USER .BASED ON THE SAME CONCEPT IN 1969 ,UNICS OPERATING SYSTEM WAS DEVELOPED FOR 100'S OF USERS.UNICS STANDS FOR UNIPLEXED INFORMATION COMPUTING SYSTEM.INITIALLY UNICS WAS WRITTEN ASSEMBLY LANGUAGE.IN 1973,THEY REWRITTEN IN 'C' LANGUAGE NAMED AS UNIX.

SALIENT FEATURES OF UNIX:

1.MULTI USER CAPABILITY

2.MULTI TASKING CAPABILITY

3.PROGRAMMING FACILITY

4.PORTABILITY

5.COMMUNICATION(ELECTRONICS MAIL)

6.SECURITY

7.OPEN SYSTEM

8.SYSTEM CALLS

9.HELP FACILITY

MULTI USER:

MULTI USER OPERATING SYSTEM MEANS MORE THAN ONE USER SHARES THE SAME SYSTEM RESOURCES (HARD DISK,MEMORY,PRINTER,APPLICATION SOFTWARE ETC......) AT THE SAME TIME.

MULTI TASKING:

ANOTHER HIGHLIGHT OF UNIX IS THAT IT IS MULTITASKING,IMPLYING THAT IT IS CAPABLE OF CARRYING OUT MORE THAN ONE JOB AT THE SAME TIME.IT ALLOWS YOU TYPE IN A PROGRAM IN ITS EDITIOR WHILE IT SIMULTANEOUSLY EXECUTES SOME OTHER COMMAND YOU MIGHT HAVE GIVEN EARLIER,SAY TO SORT AND COPY A HUGE FILE.THE LATTER JOB IS PERFORMED IN THE 'BACKGROUND',WHILE IN THE 'FOREGROUND' YOU USE EDITOR .OR TAKE A DIRECTORY LISTING OR WHATEVER ELSE.

DEPENDING ON THE PRIORITY OF THE TASK,THE OPERATING SYSTEM APPROPRIATELY ALLOTS SMALL TIME SLOTS(OF THE ORDER OF MILLISECONDS OR MICROSECONDS) TO EACH FOREGROUND AND BACKGROUND TASK.

PROGRAMMING FACILITY:

UNIX O/S PROVIDES SHELL.SHELL WORKS LIKE A PROGRAMMING LANGUAGE.IT PROVIDES COMMANDS AND KEY WORDS.BY RUNNING THESE TWO,USER CAN PREPARE EFFICIENT PROGRAM.

PORTABILITY:

ONE OF THE MAIN REASONS FOR THE UNIVERSAL POPULARITY OF UNIX IS THAT IT CAN BE PORTED TO ALMOST ANY COMPUTER SYSTEM,WITH ONLY THE BARE MINIMUM OF ADOPTIONS TO SUIT THE GIVEN COMPUTER ARCHITECTURE.IT WORKS WITH 8088 PROCESSORS TO SUPER COMPUTERS.

COMMUNICATION:

UNIX PROVIDES ELECTRONIC MAIL.THE COMMUNICATION MAY BE WITHIN THE NETWORK OF A SINGLE MAIN COMPUTER,OR BETWEEN TWO ARE MORE SUCH COMPUTER NETWORKS.THE USER CAN EASILY EXCHANGE MAIL,DATA ,PROGRAMS THRO SUCH NETWORKS.YOU MAY BE TWO FEET AWAY OR TWO THOUSANDS MILES YOUR MAIL WITH HARDLY TAKE ANY TIME TO REACH ITS DESTINATION.

SECURITY:

UNIX PROVIDES THREE LEVELS OF SECURITY TO PROTECT DATA.THE FIRST IS PROVIDED BY ASSIGNING PASSWORDS AND LOGIN NAMES TO INDIVIDUAL USERS ENSURING THAT NOT ANYBODY CAN COMESAND HAVE ACCESS TO YOUR WORK.

AT THE FILE LEVEL,THERE ARE READ ,WRITE AND EXECUTE PERMISSIONS TO EACH FILE WHICH DECIDE WHO CAN ACCESS A PARTICULAR FILE ,WHO CAN MODIFY IT AND WHO CAN EXECUTE IT.LASTLY ,THERE IS FILE ENCRYPTION.THIS ENCODES YOUR FILE INTO AN UNREADABLE FORMAT,SO  THAT EVEN IF SOME ONE SUCCEEDS IN OPENING IT,YOUR SECRETS ARE SAFE.

OPEN SYSTEM:

THE SOURCE CODE FOR THE UNIX SYSTEM,AND NOT JUST THE EXECUTABLE CODE,HAS BEEN MADE AVAILABLE TO USERS AND PROGRAMMERS.BECAUSE OF THIS MANY PEOPLE HAVE BEEN ABLE TO ADAPT THE UNIX SYSTEM IN DIFFERENT WAYS.THIS OPENNESS HAS LED TO THE INTRODUCTION OF A WIDE RANGE OF NEW FEATURE AND VERSIONS CUSTOMIZED TO MEET SPECIAL NEEDS.IT HAS BEEN EASY FOR DEVELOPERS TO ADAPT TO UNIX ,BECAUSE THE COMPUTER CODE FOR THE UNIX SYSTEM IS STRAIGHT FORWARD ,MODULAR AND COMPACT.

SYSTEM CALLS:

PROGRAMS INTERACT WITH THE KERNAL THROUGH APPROXIMATELY 100 SYSTEM CALLS.

SYSTEM CALLS TELL THE KERNEL TO CARRY OUT VARIOUS TASKS FOR THE PROGRAM ,SUCH AS OPENING A FILE ,WRITING TO A FILE,OBTAINING INFORMATION ABOUT A FILE,EXECUTING A PROGRAM,TERMINATING A PROCESS CHANGING THE PRIORITY OF A PROCESS ,AND GETTING THE TIME OF DAY .DIFFERENT IMPLEMENTATIONS OF UNIX SYSTEM HAVE COMPATIBLE SYSTEM CALLS,WITH EACH CALL HAVING THE FUNCTIONALITY.HOWEVER THE INTERNALS,PROGRAMS THAT PERFORM THE FUNCTIONS OF SYSTEM CALLS(USUALLY WRITTEN IN THE C LANGUAGE).

HELP FACILITY:

UNIX PROVIDES MANUAL PAGES FOR UNIX COMMANDS.