ch 05 rev after adding

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5.1

55

ComputerComputerOrganizationOrganization

First PartFirst Part

Foundations of Computer Science Cengage Learning


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5.2

List the three subsystems of a computer.

Describe the role of the central processing unit (CPU).

Describe the fetch-decode-execute phases of a cycle.

Describe the main memory and its addressing space.

Define the input/output subsystem.

Understand the interconnection of subsystems.

Describe different methods of input/output addressing.

Distinguish the two major trends in the design of computers.

Understand how computer throughput can be improved

using pipelining and parallel processing.

ObjectivesObjectives

After studying this chapter, the student should be ableAfter studying this chapter, the student should be able

to:to:


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5.3

WeWe cancan dividedivide thethe partsparts thatthat makemake upup aa computercomputer intointo

threethree broad broad categoriescategories oror subsystemsubsystem:: thethe centralcentral

processingprocessing unitunit (CPU)(CPU),, thethe mainmain memorymemory andand thetheinput/outputinput/output subsystemsubsystem..

Figure 5.1 Computer hardware (subsystems)


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5.4

55--1 CENTRAL PROCESSING UNIT1 CENTRAL PROCESSING UNIT

TheThe centralcentral processingprocessing unitunit (CPU)(CPU) performsperforms

operationsoperations onon datadata.. InIn mostmost architecturesarchitectures itit hashas threethree

partsparts:: anan arithmeticarithmetic logiclogic unitunit (ALU)(ALU),, aa controlcontrol unitunit

andand aa setset ofof registersregisters-- fastfast storagestorage locationslocations (Figure5.2)..


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5.5

Figure 5.2 Central processing unit (CPU)


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5.6

5.1.1 -The arithmetic logic unit (ALU)

The arithmetic logic unit (ALU) performs logic, shift and

arithmetic operations on data as discussed in Chapter 4.


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5.7

5.1.2- Registers

Registers are fast stand-alone storage locations that hold data

temporarily. Multiple registers are needed to facilitate theoperation of the CPU. Some of these registers are shown in

Figure 5.2.

Data registers

Instruction register

Program counter


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5.8

Data registers 1- to speed up the CPUs operations2- required to hold the intermediateresults

3- named R1 to Rn

Instruction registers Computers store not only data, but alsoprograms. The CPU :1) Fetch instructions one by one from memory2) Store them in IR

3) Decode them4) Execute them

Program counter 1) Keeps track of the instruction currently being

executed2) After execution, it is incremented to point tothe address of the next instruction inmemory


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5.9

5.1.3- The control unit

The third part of any CPU is the control unit. The control

unit controls the operation of each subsystem. Controlling is

achieved through signals sent from the control unit to other

subsystems.


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5.10

55--2 MAIN MEMORY2 MAIN MEMORY

MainMain memorymemory isis thethe secondsecond majormajor subsystemsubsystem inin aa

computercomputer (Figure(Figure 55..33)).. ItIt consistsconsists ofof aa collectioncollection ofof

storagestorage locations,locations, eacheach withwith aa uniqueunique identifier,identifier, calledcalled

anan addressaddress.. DataData isis transferredtransferred toto andand fromfrom memorymemory iningroupsgroups ofof bitsbits calledcalled wordswords.. AA wordword cancan bebe aa groupgroup ofof 88

bits,bits, 1616 bits,bits, 3232 bitsbits oror 6464 bitsbits (and(and growing)growing).. IfIf thethe

wordword isis 88 bits,bits, itit isis referredreferred toto asas aa bytebyte.. TheThe termterm

bytebyte isis soso commoncommon inin computercomputer sciencescience thatthatsometimessometimes aa 1616--bitbit wordword isis referredreferred toto asas aa 22--bytebyte word,word,

oror aa 3232--bitbit wordword isis referredreferred toto asas aa 44--bytebyte wordword..


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5.11Figure 5.3 Main memory


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5.12

- - Address space

To access a word in memory requires an identifier. Althoughprogrammers use a name to identify a word (or a collection

of words), at the hardware level, each word is identified by

an address. The total number of uniquely identifiable

locations in memory is called the address space. Forexample, a memory with 64 kilobytes and a word size of 1

byte has an address space that ranges from 0 to 65,535.


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5.13

Memory addresses are defined using unsigned

binary integers.

i

If a computer has N words of memory, we need an unsigned integer

of size Log2 N bits to refer to each memory locations.


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5.14

Example 5.1

AA computercomputer hashas 3232 MBMB (megabytes)(megabytes) ofof memorymemory.. HowHow manymany bitsbits

areare neededneeded toto addressaddress anyany singlesingle bytebyte inin memory?memory?SolutionSolution

TheThe memorymemory addressaddress spacespace isis 3232 MB,MB, oror 222525 ((2255 222020)).. ThisThis

meansmeans thatthat wewe needneed loglog22 222525,, oror2525 bitsbits,, toto addressaddress eacheach bytebyte..

Example 5.2

AA computercomputer hashas 128128 MBMB ofof memorymemory.. EachEach wordword inin thisthis computercomputer

isis eighteight bytesbytes.. HowHow manymany bitsbits areare neededneeded toto addressaddress anyany singlesingle

wordword inin memory?memory?

SolutionSolution

TheThe memorymemory addressaddress spacespace isis 128128 MB,MB, whichwhich meansmeans 222727..

However,However, eacheach wordword isis eighteight ((2233)) bytes,bytes, whichwhich meansmeans thatthat wewe

havehave 222424 wordswords.. ThisThis meansmeans thatthat wewe needneed loglog22 222424,, oror2424 bitsbits,, toto

addressaddress eacheach wordword..


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5.15

Random access memory (RAM)

Makes up most of the main memory.

Data item can be accessed randomly using the address .

Can be read from and written to. It is volatile.

Read-only memory (ROM)

Written by the manufacturer. Can read from but not write to.

It is nonvolatile

EX. Holding the boot program

Two main types of memory exist: RAM and ROM.

- - Memory types


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5.16

- - Memory types

Two main types of memory exist: RAM and ROM.

Random access memory (RAM)

Static RAM (SRAM)

Use flip-flop gates to hold data

Dynamic RAM (DRAM)Uses capacitors for data storage

Read-only memory (ROM)

Programmable read-only memory (PROM). Erasable programmable read-only memory (EPROM).

Electrically erasable programmable read-only memory (EEPROM).


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5.17

Memory hierarchy

Computer users need a lot of memory, especially memory

that is very fast and inexpensive. This demand is not always

possible to satisfyvery fast memory is usually not cheap. A

compromise needs to be made. The solution is hierarchical

levels of memory.

Figure 5.4 Memory hierarchy


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5.18

Cache memory

Cache memory is faster than main memory, but slower than

the CPU and its registers. Cache memory, which is normally

small in size, is placed between the CPU and main memory

(Figure 5.5).

Figure 5.5 Cache memory

Cache memory at any time contains a copy of a portion of main memory.


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5.19

55--3 INPUT/OUTPUT SUBSYSTEM3 INPUT/OUTPUT SUBSYSTEM

TheThe thirdthird majormajor subsystemsubsystem inin aa computercomputer isis thethe

collectioncollection ofof devicesdevices referredreferred toto asas thethe input/outputinput/output

(I/O)(I/O) subsystemsubsystem.. ThisThis subsystemsubsystem allowsallows aa computercomputer toto

communicatecommunicate withwith thethe outsideoutside worldworld andand toto storestoreprograms programs andand datadata eveneven whenwhen thethe power power isis offoff..

Input/outputInput/output devicesdevices cancan be be divideddivided intointo twotwo broadbroad

categoriescategories:: nonnon--storagestorage andand storagestorage devicesdevices..


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5.21

Storage devices

Storage devices, although classified as I/O devices, can store

large amounts of information to be retrieved at a later time.

They are cheaper than main memory, and their contents are

nonvolatilethat is, not erased when the power is turned off.

They are sometimes referred to as auxiliary storage devices.

We can categorize them as eithermagnetic oroptical.


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5.22

Magnetic storage devices:

1- Magnetic disks.

Figure 5.6 A magnetic disk


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Figure 5.7 A magnetic tape

Magnetic storage devices:

2- Magnetic tape.

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