II. Computer System Structure

1. Interrupt Based System1) Physical IOCS vs. Logical IOCS Relation

PROBLEM PROG

LOGICAL

IOCS

PHYSICAL IOCS

INPUT

DEVICE

Issue GET

Next instruction

Provide record and return toprob. prog

ORIF I/O required WAIT

When I/o completereturn to problemprogram

(channel scheduler)

Determine channelif channel busythen return to logical IOCS

If channel not busyissue START I/Oand return to Logical IOCS

When I/O complete

I/O START

I/O complete

II. Computer System Structure

2) A kind of Interrupt- External Interrupt

: Timer, Key on Console , Signal from other process

- SVC Interrupt: Super Visor Call Interrupt

- I/O Interrupt : I/O completion or Error occurrence

- Machine Check : Error of machine in System

- Program Check : Execution Error of Program

( Divide by 0 , Error instruction)

II. Computer System Structure

3) The Processing of Interrupt

Program begin

Interrupt begin

Interrupt execute

Interrupt complete

Program

Interrupt process routine

II. Computer System Structure

System Operation User mode

Monitor mode - Supervisor mode

- System mode

Dual-mode operation ( Context Switching ) ex) Program execution (1) (3) Program execution

User mode

System mode(2) Interrupt execution

II. Computer System Structure

4) Relation of New, Current and Old_PSW in INTERRUPT - I

SUPVR PRG 74

PRGIOIADD A, B

ADD C, K

Location of next instruction

Current PSW

New PSW Old PSW

PRGIOI

009138

PRGEXT

PRGSVC

PRGPCK

PRGMCK

PRGIOI 009138

58

60

68

70

78

18

20

28

30

38

21

4

3

II. Computer System Structure

4) Relation of New, Current and Old_PSW in INTERRUPT - II

6

SUPVR PRG 74

PRGIOIADD A, B

ADD C, K

Location of next instruction

Current PSW

New PSW Old PSW

009138

PRGEXT

PRGSVC

PRGPCK

PRGMCK

PRGIOI 009138

58

60

68

70

78

18

20

28

30

38

78

5

II. Computer System Structure

2. I/O Interrupt1) Processing I/O Requests Relationship

- Without I/O interruption

SYSTEMin wait state

1 2 3 4 5 6

F1

F2

F3

SUPVR

I/O

processingI/O wait

Waiting for I/O completion

processingI/O wait

Waiting for I/O completion

processing

I/O wait

task selection task selection task selection

ALL BOUND

Active stateInactive state

II. Computer System Structure

- Case of I/O interruptI/O interrupt sequence

F1 : s I/O interrupt occurs

F2 : s I/O interrupt occurs

F3 : s I/O interrupt occurs

Waiting for I/O

Waiting for I/O Waiting to be selected

F1

F2

F3

Waiting for I/O

SUPVRPosting Traffic Bit & Performing Task Selection

Waiting to be selected

Systemin wait state

F1 F2 F3

I/O interrupts

II. Computer-System Structure

3. Storage Structure

Main-memory : volatile storage device ( Register, cache )

Magnetic Disk : sectors track cylinder package

Magnetic Tape : backup, infrequently, transfering

track

sector

cylinder

platter

rotation arm

actuatorRead-write head

II. Computer-System Structure

1) Storage Hierarchy- Caching : by cache size, replacement policy 80~99%

- internal programmable registerex) index register, Accumulator

- cache coherency & consistency (a copy of A ) in a multiprocessor

in a distributed environment

Register

cache

main memory

electronic disk

magnetic disk

optical disk

magnetic tapes

Storage Hierarchy

II. Computer-System Structure

2) H/W Protection : for system utilization- To share system resources

SPOOL

multiprogramming

- Dual mode operation

user mode

monitor mode supervisor mode

system mode

privileged mode

privileged instruction : executed in busy monitor mode

ex) I/0 instruction , Timer ...

II. Computer-System Structure- Memory protection

Base registerLimit register

A base and a limit register

define a logical address space.

Monitorjob 1

job 2

job 3

job 4

0

256000

300040

420940

8800001024000

300040

120900base register

limit register

base + limit

trap to operating system

monitor - addressing error

CPU address yes yes

no no

memory

base Hardware address protection

with base and limit registers.

II. Computer-System Structure

- CPU protection : Infinite loop - Timer : Control OS X

- System Call (monitor call) : Process OSInterface

Use of a system call to perform I/O.

Case n

read

system call n

perform I/O

residentmonitor

user program

returnto user

trap to monitor

II. Computer-System Structure

3 ) Multiprocessor Systems- Throughput : n processor n speed up ratio

- Reliability

- fail-soft : 1 gain in 10 processor graceful degradation

Symmetric multiprocessing : Same O.S copy

ex) Tandem system

Asymmetric multiprocessing : a master processor with slave processors

Speed up

n