Comput er Syst em Overview I nt roduct ion A comput er syst em - - PowerPoint PPT Presentation

Comput er Syst em Overview

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I nt roduct ion

• A comput er syst em consist s of

– har dwar e – syst em pr ogr ams – applicat ion pr ogr ams

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Oper at ing Syst em

• Pr ovides a set of ser vices t o syst em user s (collect ion
• f ser vice pr ogr ams)
• Shield bet ween t he user and t he har dwar e
• Resour ce manager :

– CPU(s) – memor y and I / O devices

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Comput er syst em over view: st ar t ing f r om 0 Basic f unct ionalit y of a comput er syst em: I nst r uct ion Cycle

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A closer -t o-r ealit y-view of t odays’ pr ocessor s (a) A t hr ee-st age pipeline (b) A super scalar CPU (c – to appear) Multicore CPUs

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Basic Element s of a Comput er Syst em

• Pr ocessor + r egist er s
• Main Memor y (“r eal” or

pr imar y memor y) – volat ile

• I / O modules

– secondar y memor y devices – communicat ions equipment – t er minals

• Syst em bus

– communicat ion among pr ocessor s, memor y, and I / O modules

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Regist er s: 1. User -Visible

• May be r ef er enced by machine lang.

– By bot h applicat ion and syst em programs

• Enable pr ogr ammer t o minimize main-

memor y r ef er ences by opt imizing r egist er use

• Types of user -visible r egist er s

– Dat a – Addr ess

• I ndex: f or indexed addressing,
• f f set
• St ack point er: f or procedure calling

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Regist er s: 2. Cont r ol and St at us

• Used by

– pr ocessor t o cont r ol execut ion – oper at ing-syst em t o cont r ol t he execut ion of pr ogr ams

• Basic C&S r egist er s:

– Program Count er (PC)

• Cont ains t he address of an

inst ruct ion t o be f et ched – I nst ruct ion Regist er (I R)

• Cont ains t he inst ruct ion most

recent ly f et ched – Program St at us Word (PSW)

• condit ion codes (posit ive/ negat ive/

zero result , overf low, … )

• I nt errupt enable/ disable
• Supervisor/ user mode

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I nst r uct ion Cycle r evisit

• Pr ocessor f et ches inst r uct ion f r om memor y

– Program count er (PC) holds address of inst ruct ion t o be f et ched next ; PC is increment ed af t er each f et ch – Fet ched inst ruct ion is placed in t he inst ruct ion regist er

• Types of inst r uct ions

– Pr ocessor -memor y – Pr ocessor -I / O – Dat a pr ocessing – Cont r ol: alt er sequence of execut ion

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I s t hat enough f or ....

• Component s of a simple personal comput er

Monitor

Bus

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I nt errupt s!

• An int errupt ion of t he normal sequence of

execut ion! Why?

– Somet hing went wr ong (div. by 0, r ef er ence

• ut side user ’s memor y space, har dwar e f ailur e,…

) – Timer – I / O

• and t hen?

– I nt er r upt handler t akes cont r ol:

• a pr ogr am t hat det er mines t he nat ur e of t he

int er r upt and per f or ms what ever act ions ar e needed

• gener ally par t of t he oper at ing syst em

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I nt er r upt Cycle

• Pr ocessor checks f or int er r upt s
• I f no int er r upt s f et ch t he next inst r uct ion f or t he

cur r ent pr ogr am

• I f an int er r upt is pending, suspend execut ion of t he

cur r ent pr ogr am, and execut e t he int er r upt handler

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Cont r ol f low wit h int er r upt s

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What happens

(a) St eps in st art ing an I / O device and get t ing int errupt (b) How t he CPU is int errupt ed

(a) (b)

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I nt er r upt s as suppor t f or I / O

Not e:

• I nt er r upt s allow t he pr ocessor t o execut e ot her

inst r uct ions while an I / O oper at ion is in pr ogr ess

• I mpr ove pr ocessing ef f iciency

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I nt er r upt -Dr iven I / O

• Pr ocessor is int er r upt ed when I / O

module r eady t o exchange dat a

• Pr ocessor is f r ee t o do ot her wor k
• No needless wait ing

BUT:

• St ill consumes a lot of pr ocessor

t ime because ever y wor d r ead or wr it t en passes t hr ough t he pr ocessor How about using DMA …

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I / O using Dir ect Memor y Access (DMA)

• The pr ocessor is only involved at

t he beginning and end of t he t r ansf er

– Pr ocessor gr ant s I / O (DMA) module aut hor it y t o r ead f r om or wr it e t o memor y a block of dat a – An int er r upt is sent when t he t ask is complet e

• Pr ocessor is f r ee t o do ot her

t hings

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Mult iple I nt er r upt s Q: To int er r upt an int er r upt ?

1. Sequent ial Or der : af t er int er r upt handler complet es, pr ocessor checks f or addit ional int er r upt s 2. Pr ior it ies: High pr ior it y int er r upt s:

• cause lower -pr ior it y

int er r upt s t o wait – cause a lower -pr ior it y int er r upt handler t o be int er r upt ed – Example: when input ar r ives f r om communicat ion line, it needs t o be absor bed quickly t o make r oom f or mor e input

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Comput er Hardware Review (7)

St ruct ure of a large Pent ium syst em

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Cache Memory

• I ncrease t he speed of memory

– Pr ocessor speed is higher t han memor y speed

Hit : t he inf ormat ion was in cache; else, miss

• I nvisible t o operat ing syst em

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Cache Design: I mpor t ant issues

• 1. Cache size
• 2. Block size
• 3. Mapping f unct ion
• det ermines which cache locat ion t he

block will occupy

• 4. Replacement algorit hm
• det ermines which block t o replace

(e.g. Least -Recent ly-Used (LRU) algorit hm)

• 5. Writ e policy
• Can occur every t ime block is updat ed
• Can occur only when block is replaced

– Minimizes memory operat ions – Leaves memory in an obsolet e st at e

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Memor y Hier ar chy

Going Down t he Hier ar chy

• I ncr easing capacit y, I ncr easing access

t ime

• Decr easing cost per bit , Decr easing

f r equency of access of t he memor y

– localit y of ref erence: during program execut ion memory addresses t end t o clust er (it erat ion loops, subrout ines, … )

Operat ing Syst em Overview

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Layers of Comput er Syst em

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Oper at ing Syst em – OS obj ect ives

• Pr ovides a set of ser vices

t o syst em user s

• Shield bet ween t he user

and t he har dwar e

• Resour ce manager :

– CPU(s) – memor y and I / O devices

• Convenience

– Makes t he comput er mor e convenient t o use

• Ef f iciency

– Allows comput er syst em r esour ces t o be used in an ef f icient manner

• Abilit y t o evolve

– Per mit int r oduct ion of new syst em f unct ions wit hout int er f er ing wit h ser vice

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Ser vices Pr ovided by t he Oper at ing Syst em

• Pr ogr am execut ion:

– CPU scheduling, resource (memory) allocat ion and management , synchronizat ion

• Access t o I / O devices

– Unif orm int erf aces, hide det ails, opt imise resources (disk scheduling)

• Cont r olled access t o f iles

– And st ruct ure of dat a

• Syst em/ r esour ce access

– Aut horizat ion, prot ect ion, allocat ion

• Ut ilit ies, e.g. f or pr ogr am development

– Edit ors, compilers, debuggers

• Er r or det ect ion and r esponse, when, e.g.

– hardware, sof t ware errors – operat ing syst em cannot grant request of applicat ion

• Monit or ing, account ing

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Oper at ing Syst em: … (r oughly) it is a pr ogr am …

• r elinquishes

cont r ol of t he pr ocessor t o execut e ot her pr ogr ams OS Ker nel:

• (r oughly) por t ion
• f OS t hat is in

main memor y

• Cont ains most -

f r equent ly used f unct ions

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Some hist or y: Evolut ion of Oper at ing Syst ems

• Har dwar e upgr ades, new t ypes of har dwar e, enabled

f eat ur es

• New ser vices, new needs

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OS hist ory: bef ore t he st one age

Ser ial Pr ocessing

• No oper at ing syst em
• Machines r un f r om a console wit h display light s and

t oggle swit ches, input device, and pr int er

• Schedule t ome
• Set up included

– loading t he compiler , sour ce pr ogr am, – saving compiled pr ogr am – loading – linking

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OS hist or y: f ir st “t ools” appear Simple Bat ch Syst ems:

• Monit or s

– Sof t war e t hat cont r ols t he r unning pr ogr ams – Bat ch j obs t oget her – Pr ogr am br anches back t o monit or when f inished – Resident monit or is in main memor y and available f or execut ion

• J ob Cont r ol Language (J CL)

– Pr ovides inst r uct ion t o t he monit or

• what compiler t o use
• what dat a t o use

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OS hist or y: Har dwar e Feat ur es…

… which made t he f irst t ools possible:

• Memor y pr ot ect ion

– do not allow t he memor y ar ea cont aining t he monit or t o be alt er ed

• Pr iviledged inst r uct ions

– Only f or monit or, e.g. f or int erf ace wit h I / O devices

• I nt er r upt s

– Mechanisms f or t he OS t o r elinquish cont r ol and r egain it

• Timer

– pr event s a j ob f r om monopolizing t he syst em

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OS hist or y: Uni/ mult i-pr ogr amming

f rom uniprogramming… .

Pr ocessor must wait f or I / O inst r uct ion t o complet e bef or e pr oceeding

… t o Mult iprogramming

When one j ob needs t o wait f or I / O, t he pr ocessor can swit ch t o t he ot her j ob

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Early bat ch syst em

– bring cards t o 1401 – read cards t o t ape – put t ape on 7094 which does comput ing – put t ape on 1401 which print s out put

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OS hist or y: Mult ipr ogr amming, Time Shar ing Time shar ing syst ems use mult ipr ogr amming t o handle mult iple int er act ive j obs

• Pr ocessor’s t ime is shar ed among mult iple user s
• Mult iple user s simult aneously access t he syst em

t hr ough t er minals

Batch Multiprogramming Time Sharing Principal objective Maximize processor use Minimize response time Source of directives to

• perating system

Job control language commands provided with the job Commands entered at the terminal

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OS hist or y: mult ipr ogr amming needs …

• …

memor y management !

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Summary: evolut ion

• First generat ion 1945 - 1955

– vacuum t ubes, plug boards

• Second generat ion 1955 - 1965

– t ransist ors, bat ch syst ems

• Third generat ion 1965 – 1980

– I Cs and mult iprogramming

• Fourt h generat ion 1980 – present

– personal comput ers

• More cont emporary present :

– Personal comput ers become parallel

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Zooming in a f ew key services The main j ob of OS is t o: run processes! ...

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Process:t he concept

Pr ocess = a pr ogr am in execut ion

• Example pr ocesses:

– OS ker nel – OS shell – Pr ogr am execut ing af t er compilat ion – www-br owser

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Process: I mplement at ion Consist s of t hree component s

• An execut able program
• Associat ed dat a needed

by t he program

• Execut ion cont ext of

t he program

– All inf or mat ion t he

• per at ing syst em needs t o

manage t he pr ocess

Execut ion cont ext

• f t he pr ogr am

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Processes creat e ot her processes

• A process t ree

– A (e.g. shell) creat ed t wo child processes, B (e.g. browser) and C (print ) – B creat ed t hree child processes, D, E, and F (various browser services/ windows)

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Procs need: synchronizat ion, ...

Two processes connect ed by a pipe

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… , t o get CPU t ime and ot her resources, …

Goals when allocat ing r esour ces t o pr ocesses:

• Fair ness and Dif f er ent ial r esponsiveness

– give f air access t o all pr ocesses – discr iminat e bet ween dif f er ent classes of j obs

• Ef f iciency

– maximize t hr oughput , minimize r esponse t ime, and accommodat e as many user s as possible

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... t o get resources wit hout deadlock, ... (a) A pot ent ial deadlock. (b) an act ual deadlock.

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..., t o do I O, access f iles, ...

I mport ant issues:

• Organizat ion of inf ormat ion
• Ef f icient access

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… , t o get memory

Memory Management

I mpor t ant issues:

• Pr ocess isolat ion

– Pr event int er f er ence bet ween dif f er ent pr ocesses – Pr ot ect ion and access cont r ol when shar ing memor y

• Allocat ion

– Cr eat e, dest r oy modules dynamically – Suppor t f or modular pr ogr amming – Ef f iciency, good ut ilizat ion

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Virt ual Memory

• Allows pr ogr ammer s t o addr ess memor y f r om a logical

point of view (wit hout wor r ying about t he physical availabilit y)

• Tr ansf er memor y disk: t r anspar ent t o t he

pr ocesses

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Maj or Element s of an Operat ing Syst em

• OS = ver y lar ge piece of

sor t war e!

• Component s: decompose a

pr oblem int o mor e manageable subpr oblems (pr ocess manager , f ile manager , et c)

• Boot st r ap pr ogr am act ivat es

OS ker nel (per manent syst em pr ocess)

– Shell ( kernel): program t o let t he user init iat e processes

• User or syst em pr ogr ams

make dir ect use of t he OS via syst em calls

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St eps in Making a Syst em Call

st eps in making t he syst em call

read (fd, buffer, nbytes)

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Some Syst em Calls

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A st ripped down shell

while (TRUE) { /* repeat forever * / type_prompt( ); /* display prompt * / read_command (command, parameters) /* input from terminal * / if (fork() != 0) { /* fork off child process * / /* Parent code * / waitpid( -1, &status, 0); /* wait for child to exit * / } else { /* Child code * / execve (command, parameters, 0); /* execute command * / } }

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I ssues in Modern Operat ing Syst ems

• Micr oker nel ar chit ect ur e

– Only f ew essent ial f unct ions in ker nel; OO design

• Mult it hr eading

– A pr ocess may consist of sever al sequent ial t hr eads of execut ion

• Concur r ent comput er syst ems

– Symmet r ic mult i-pr ocessor syst ems – Mult i-t hr eaded/ mult icor e pr ocessor s – Dist r ibut ed syst ems

• provide t he illusion of a single main memory and single

secondary memory space in clust er-based plat f orms

• Real-t ime Oper at ing Syst ems

– For t ime-cr it ical applicat ions, mult imedia, …

• Embedded Oper at ing Syst ems

– Const r aint s: limit ed r esour ces, special f unct ionalit ies

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Microkernel

• Small OS cor e; cont ains only essent ial OS f unct ions:

– Low-level memory management (address space mapping) – Process scheduling – I / O and int errupt management

• Many ser vices t r adit ionally included in t he OS ker nel ar e now

ext er nal subsyst ems

– device drivers, f ile syst ems, virt ual memory manager, windowing syst em, securit y services

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Benef it s of a Microkernel Organizat ion

• Unif or m int er f ace on r equest made by a pr ocess

– All services are provided by means of message passing

• Dist r ibut ed syst em suppor t

– Message are sent wit hout knowing what t he t arget machine is

• Ext ensibilit y

– Allows t he addit ion/ removal of services and f eat ures

• Por t abilit y

– Changes needed t o port t he syst em t o a new processor is changed in t he microkernel - not in t he ot her services

• Obj ect -or ient ed oper at ing syst em

– Component s are obj ect s wit h clearly def ined int erf aces t hat can be int erconnect ed

• Reliabilit y

– Modular design; – Small microkernel can be rigorously t est ed

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Concurrent Comput er Syst ems

each instruction executed on a dif f erent set of data by the dif f erent processors a set of processors simultaneously execute dif f erent instruction sequences on dif f erent data sets

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Symmet ric Mult iprocessors (and mult icores)

• Pr ocessors shar e t he same memor y and I / Os
• Ker nel can execut e on any pr ocessor
• Scheduling & synchr onizat ion, memor y management &

consist ency (also r esear ch issues)

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Clust er Comput er Plat f orms

• Net wor k
• Middlewar e layer (par t of OS) t o pr ovide

– single-syst em image (synchr onizat ion, consist ency, global st at es, f ile syst ems) – f ault -t oler ance, load balancing, par allelism

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I nst ant iat ion: UNI X

• Har dwar e is sur r ounded by t he oper at ing-syst em
• Oper at ing syst em is called t he ker nel
• Moder n unix ver sions (solar is) mor e complex
• Comes wit h a number of user ser vices and int er f aces

– Shell, compiler s, …

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I nst ant iat ion: Windows

• Client / Ser ver

comput ing; base f or dist r ibut ed comput ing

• Modif ied micr oker nel

ar chit ect ur e

– not a pur e micr oker nel: many syst em f unct ions

• ut side of t he

micr oker nel r un in ker nel mode – modules can be r emoved, upgr aded, or r eplaced wit hout r ewr it ing t he ent ir e syst em