Fields and columns in process table, interrupt vector

Process table: A process table contains the information related to a process. It contains information in a tabular format with columns related to: process management, file management and memory management. Fields and columns of a process table usually contain the information about:

Process management:

  • Program counter
  • Program status word
  • CPU time used
  • Parent process
  • Process group
  • Signals
  • Registers
  • Time when process started
  • Child CPU time
  • Next alarm time
  • Stack pointer
  • Process state
  • Priority
  • Scheduling parameters
  • Process ID

File management:

  • Root directory
  • Working directory
  • File descriptors
  • User ID
  • Group ID

Memory management:

  • Pointer to data segment information
  • Pointer to text segment information
  • Pointer to stack segment information

Interrupt vector: An interrupt vector has the address of interrupt service procedure. Say, a user process is running and a disk interrupt occurs. Then, program counter, registers, program status word is pushed to stack by interrupt hardware. The CPU then looks for address specified in interrupt vector. After that, new program counter is loaded by interrupt vector. Assembly language routines are then used for saving registers and setting stack pointer. Next, a high level language is used for running interrupt service. After that, scheduler is called to figure out which process has to be run next. Then, control is again given to the assembly level procedure for starting a new process.

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