The process - the meaning

                                                  THE  PROCESS



7.1  THE  MEANING
       

•  A Process  is  an abstract   concept,by  which  one  explain &  control  the  execution  of  a  program  in an OS.                         

•  It  is  defined  as  a  program  in  execution. 

•  Unix  is  a  multi-user  and  multi-tasking  system, several  programs - several  users - running at  same  time. All  Programs  share  same  CPU.

• The  Kernel  generates  processes  for  every  program under  execution & allocates  CPU  time  slots  to  these  programs.

• Each  process  have  a unique  ID,that  is  allocated  by  the  kernel &  these numbers  are  called  process identification  numbers or PIDs.

         Mathematically, a  process  is represented  by  the  tuple,
                  (process id, code, data, register values, pc value)

•  PID-- >identify  the  process  from  other  process.
• code--> program  code  under  execution.
• data--> data  used  during  execution.
• register values --> these are  values  in  CPU reg.
• pc value -->  it is  the  address in program  counter  from  where the  program  starts  or  continues.

•     At present  the  max. value of PID is 32767.

•     when  the  system  is booted,the  kernel  gets  loaded into  the memory & then gets  executed.

•      Immediately  a system  process called, the  swapper is created.

•   The PID of this process'll be  0,it creates another process called init,which means  initialiser.

•    Init  is one  of  the  first  program ,its  starts  running  after  the  boot strapping. The  PID  of init process is 1.

•    Init is  responsible for  initialising all subsequent  processes.

•    It  sets  the   user mode in either single  or  multi user. It is also  responsible  for  generating   processes on log-ins.