Wonder Shine Blog

[OS] Process - Process Concept

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The Process

From https://commons.wikimedia.org/wiki/File:Process-in-memory.jpg

Process = Program on execution
Program : Passive entity, with command lists on file
Process : Active entity, with Program counter and corresponding resources

Process State

From https://www.d.umn.edu/~gshute/os/processes-and-threads.xhtml

There are 5 steps for Process

NEW
process is on creation
RUNNING
process is executing commands
WAITING
process is waiting for some signal or IO to be completed
READY
process is waiting to be assigned to processor
TERMINATED
process is terminating

To be more specific, considering swap space there would be 2 more states:

From https://en.wikipedia.org/wiki/Process_state

SWAPPED OUT AND WAITING
process has been swapped out on waiting
SWAPPED OUT AND BLOCKED
process has been swapped out on blocked

Process Control Block

From https://cssimplified.wordpress.com/2015/11/23/process-control-block-pcb/

PCB is data structure in the operating system kernel containing the information needed to manage a particular process.
The fields varies to OS, but there are some common fields like:

Process Status
new, ready, running, waiting, etc.
Program Counter (PC)
PC points next command of the process to be executed.
CPU Registers
accumulator, index register, stack register, general purpose register, etc. These states are saved with PC on interrupt, and then restored on execution.
CPU Scheduling Infos
process priority, pointer to schedule queue and other scheduling variables.
Memory Management Infos
base register, limit register, page table, segment table, etc.
Accounting Infos
CPU use time, actual use time, time limit, account number, job or process number, etc.
IO status Infos
IO Devices on this process, opened file list, etc.

References


https://commons.wikimedia.org/wiki/File:Process-in-memory.jpg

http://www.d.umn.edu/~gshute/os/processes-and-threads.xhtml

https://stackoverflow.com/questions/28795024/who-controls-the-process-control-blockpcb/28795091

https://cssimplified.wordpress.com/2015/11/23/process-control-block-pcb/