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OPERATING SYSTEMS (THEORY)

LECTURE - 3

K.ARIVUSELVAN

 Assistant Professor Senior – SITE 

VIT University

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=> Two State Process Model

=>

=> Five State Process Model

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Two State Process Model

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Three State Process Model

Dispatch

Ready Running

Time-out

Event

OccursEvent

Wait

Waiting

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Ready Running

Running Ready

Running process has expired his time slot

Runnin rocess ets interru ted because a hi her riorit rocess is in

the ready state

unn ng a ng

 An access to a resource not yet available

a ng or a process o prov e npu

Waiting Ready

The event for which it was waiting occurs

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Five State Process Model

 

process that

is prepared to

execute

process that is

currently being

executed

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Submission of a batch job

User logs on

Created by OS to provide a service to a user

e.g., pr nt ng a e

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TWO QUEUES

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Multiple Blocked Queues

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Modes of Execution

2 Modes:

=>User Mode (Less Privileged Mode)

=>System Mode / Kernel Mode (More Privileged Mode)

Why ?

 

How ?

 

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Process Switching

When to Switch a Process?

  rap :

 –

moved to terminated state)

(2) Interrupt:

The cause is external to the execution of the current instruction – (controlis transferred to Interrupt Handler )

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Context Switch

Main Idea:

The act of swapping a process state on or off the CPU is a

con ex sw c

,

the state of the old process and load the saved state for the new

process

Context of a process represented in the PCB

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Steps in Context Switch

Save context of processor including program counter and other registers

 

other associate information

Move PCB to appropriate queue – ready, blocked

Select another rocess for execution. 

Update PCB of the selected process

Restore CPU context from that of the selected process.

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Context-switch time is overhead; the system does no useful

work while switching

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Revision

Pro ram

Process

Pro ram VS Process

Process Image PCB

rocess tates

Process Creation

Process Termination

Process Control Modes

Process switching

Context Switching