operating system overview. contents basic hardware elements

OPERATING SYSTEM

OVERVIEW

ContentsContents

Basic hardware elements

Most I/O devices

are much slower than

the processor

InterruptsInterrupts

Interrupt request signal

Active waiting cycle

(polling)

An interrupt cycle is added to the

instruction cycle (fecth and execute).

The processor checks to

see if an interrupt has

occured (interrupt signal)

Interrupt mechanismInterrupt mechanism

interrupt handler

interrupt vector

Interrupt mechanismInterrupt mechanism

CPU saves PS and PC (push) into the

control stack

CPU saves PS and PC (push) into the

control stack

CPU loads into PC and

PS the corresponding values from the

interrupt vector

CPU loads into PC and

PS the corresponding values from the

interrupt vector

Interrupt processingInterrupt processing

iretiret

interrupt handler

execution

interrupt handler

execution

Interrupt processingInterrupt processing

Interrupt enable/disable bit (PS register)Interrupt enable/disable bit (PS register)

Hardware priority

Hardware priority

STI (Set Interrupt) CLI (Clear

Interrupt)

STI (Set Interrupt) CLI (Clear

Interrupt)

Interrupt mechanismInterrupt mechanism

main memorymain memory

i+1i+1 PS inth

1OOii1OO1OO

149149

15O15O iretiret

1OOO1OOO

12OO12OO

12O112O1

main memorymain memory

inthinth

progproginterruptinterrupt

11

22

33

interrupt vectorinterrupt vector

Interrupt processing

PS prog

12O1

3824

PSPS

PCPC

SPSP

stack

main memory

38243824

39OO39OO

CPU completes execution

of the current instruction

CPU completes execution

of the current instruction

Interrupt processing

interrupt signal has been acceptedinterrupt signal has been accepted

PS inth

1OO

3822

PSPS

PCPC

SPSP

stack

main memorymain memory

38243824

39OO39OO

12O1

PS prog

38233823

38223822

Interrupt processing

PS inth

151

3822

PSPS

PCPC

SPSP

stack

main memorymain memory

38243824

39OO39OO

12O1

PS prog

38233823

38223822

iret executioniret execution

Interrupt processing

stack

main memorymain memory

38243824

39OO39OO

PS prog

12O1

3824

PSPS

PCPC

SPSP

iret completed iret completed

Interrupt processing

O.S.Components

ContentsContents

Process Management

O.S. COMPONENTS

Main-Memory Management

Secondary-Memory

Management

File Management

I/O-System Management

O.S. COMPONENTS

Creating and deleting processes

Suspending and resuming processes

Provide mechanisms

for process interaction

Process management

Keeping track of which

parts of memory

are currently being used

and by whom

Main memory management

Deciding which processes are to be loaded

when memory becomes available

Main memory management

Allocating and deallocating memory

space as needed

Main memory management

Secondary memory

management

Free space management

Storage allocation

Disk scheduling

I/O SYSTEM MANAGEMENT

The I/O subsystem

consists of

A memory-management component that

includes buffering and spooling

A general device driver interface

Drivers for specific hardware devices

A general device driver interface

Drivers for specific hardware devices

I/O SYSTEM MANAGEMENT

The I/O subsystem

consists of

I/O SYSTEM MANAGEMENT

The I/O subsystem

consists of

File management

Creating and deleting

files and directories

Supporting primitives

for manipulating file

and directory

Mapping files

onto storage

Backing up files

on stable storage media

File management

Protection systemsProtection systems

Mechanism for

controlling the access

of processes to system resources

The mechanism must

provide means for specifying the

controls

to be imposed and means for enforcement

Protection systems

The interface between users and O.S.

A program that reads

and interpretes control statements

The interface between users and O.S.

A program that reads

and interpretes control statements

Comand-Interpreter System

Its main function: to get next command

statement

and execute it (shell)

Its main function: to get next command

statement

and execute it (shell)

Comand-Interpreter System

System calls

ContentsContents

Processes communicate

with the O.S. and request services to it by

making system calls

System Calls

System calls provide

the interface between any process and O.S.

System Calls

Process control

Examples of System CallExamples of System Call

Communications

Information management

Device manipulation

File manipulation

Corresponding to

each system call

there is a library procedure

Corresponding to

each system call

there is a library procedure

count= read (file, buffer, nbytes)

count returns the number of bytes actually read

C programC program

Example: read system callExample: read system call

Library read

procedure

operating system

system call READ

INT

return from INT

register xregister x

x call parameters

load x

system call READ 2

3

1

Puts the parameters of the system call in machine

registers

Puts the parameters of the system call in machine

registers

The library procedureThe library procedure

The control is returned to the caller by

returning the status code as a result

The control is returned to the caller by

returning the status code as a result

Issues a INT instruction to start the O.S.

Issues a INT instruction to start the O.S.

directly via registers

in a memory block whose address is passed as a

parameter in a registry

into the stack (push, pop)

directly via registers

in a memory block whose address is passed as a

parameter in a registry

into the stack (push, pop)

Methods to pass parameters to operating systemMethods to pass parameters to operating system

hardware

(CPU, memory, disks, terminals, …)

UNIX O.S.

(process management, memory management, file system,

I/O, ...)

standard library

(open, close, read, write, ..)

utility programs

(shell, compiler, …)

users

user mode

kernel mode

user int.

library

interface

system

call

interf.

Dual mode of operationsDual mode of operations

user modeuser mode

Hardware control does not allow the execution of

privileged instructions

Hardware control does not allow the execution of

privileged instructions

Used for normal execution of user programs

Used for normal execution of user programs

Used for the execution of O.S. functions as

required by system calls

Used for the execution of O.S. functions as

required by system calls

supervisor mode (kernel mode)supervisor mode (kernel mode)

All instructions can be executed

All instructions can be executed

Dual mode of operationsDual mode of operations