PROCESS MANAGEMENT

DEFN OF PROCESS – A PROGRAM UNDER EXECUTION, WHICH COMPETES FOR THE CPU TIME & OTHER RESOURCES

CPU Switch From Process to Process

Diagram of Process State

PROCESS CONTROL BLOCK (PCB)

* OS MAINTAINS INFORMATION OF EACH PROCESS IN A RECORD OR DATA STRUCTURE CALLED PCB

EACH USER PROCESS HAS A PCB. IT IS CREATED WHEN A USER CREATES

A PROCESS & IT IS REMOVED FROM THE SYSTEM WHEN THE PROCESS IS KILLED.

ALL THESE PCBs ARE KEPT IN MEM RESERVED FOR THE OS.

PROCESS CONTROL BLOCK (PCB)

PROCESS – ID

PROCESS STATE

PROCESS PRIORITY

REG SAVE AREA FOR PC, IR, SP

PTR’ TO PROCESS MEM

PTR’ TO OTHER RESOURCES

LIST OF OPEN FILES

ACCOUNTING INFORMATION CPU TIME CONNECT TIME etc

OTHER INFORMATION IF REQUIRED BFD OF (CURRENT DIR etc)

PTR’ TO OTHER PCB’

Ex: OS MAINTAINS 4 Q’ OR LISTS OF RUNNING PRS RDY PRS BLOCKED PRS & FREE PCB’

PROCESS ID

PRIOR

PROCESS STATE

PSW

CPU REGS

EVENT INFORMATION

MEM ALLOCN

RESOURCES HELD

PCB PTR

DHAMDHARE

OPERATIONS ON A PROCESS

CREATE A PROCESS

KILL A PROCESS

DISPATCH

CHANGE PRIORITY OF A PROCESS

BLOCK A PROCESS

TIME –UP

WAKE – UP

CREATE A PROCESS

BEGIN 0 READ CUST – FILE ADD ….. 7 DIV…… 8 ………. 9 CALL “SORT” 10 ADD……….

1 ALL CPU REGS ARE SAVED BEFORE A NEW CHILD PROCESS IS CREATED & A PCB IS ALLOCATED TO IT.

2 THE OS CONSULTS LIST OF FREE PCBs’ & ACQUIRES A FREE PCB. PCB NO 8 IN FIG.

3 ASSIGNS PID = 8 FOR NEW PROCESS

4 UPDATES FREE PCB HEADER

1 9

5 OS COUSULTS IM FOR LOCN… OF SUB – PROGR.. ( STARTING ADDRS etc)

6 OS CONSULTS MM TO DET AVAIL ABILITY OF FREE MEM & ALLOCATES THOSE LOCNS

7 OS REQUESTS IM TO LOAD THE PROGR IN THE ALLOCATED MEM LOCNS

8 PRIORITY

9 PCB FIELDS OF PCB 8 ARE INITIALIZED10 OS LINKS THIS PCB IN THE LIST OF RDY

PROCESSES. ROUND ROBIN (13,4,14,7,8)PRIORITY – etc

PRESUMING HIGHEST PRIORITY RDY- 8,13,4,14,7

5 OS COUSULTS IM FOR LOCN… OF SUB – PROGR.. ( STARTING ADDRS etc)

6 OS CONSULTS MM TO DET AVAIL ABILITY OF FREE MEM & ALLOCATES THOSE LOCNS

7 OS REQUESTS IM TO LOAD THE PROGR IN THE ALLOCATED MEM LOCNS

8 PRIORITY