process table

process table

   <operating system, process> A table containing all of the
   information that must be saved when the {CPU} switches from
   running one {process} to another in a {multitasking} system.

   The information in the process table allows the suspended
   process to be restarted at a later time as if it had never
   been stopped.  Every process has an entry in the table.  These
   entries are known as {process control blocks} and contain the
   following information:

   process state - information needed so that the process can be
   loaded into memory and run, such as the {program counter}, the
   {stack pointer}, and the values of {registers}.

   memory state - details of the memory allocation such as
   pointers to the various memory areas used by the program

   resource state - information regarding the status of files
   being used by the process such as {user ID}.

   Accounting and scheduling information.

   An example of a UNIX process table is shown below.

    SLOT  ST  PID  PGRP  UID  PRI  CPU  EVENT  NAME  FLAGS
     0    s    0     0     0   95   0  runout  sched load sys
     1    s    1     0     0   66   1    u     init  load
     2    s    2     0     0   95   0  10bbdc  vhand load sys

   SLOT is the entry number of the process.

   ST shows whether the process is paused or sleeping (s), ready
   to run (r), or running on a {CPU} (o).

   PID is the {process ID}.

   PGRP is the {process Group}.

   UID is the {user ID}.

   PRI is the priority of the process from 127 (highest) to 0
   (lowest).

   EVENT is the {event} on which a process is paused or
   sleeping.

   NAME is the name of the process.

   FLAGS are the process {flags}.

   A process that has died but still has an entry in the process
   table is called a {zombie process}.

   (1998-04-24)