08 - the processor - students version

7/24/2019 08 - The Processor - Students Version

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Y. C. Lemard

COMPUTER SCIENCE - UNIT ONE

MODULE 1 - COMPUTER ORGANISATION

THE PROCESSOR

The processor or central processing unit(CPU) is a silicon chip containing the electronic

circuits capable of executing instructions. Microcomputers typically contain one

microprocessor (ery tiny processor) and this accounts for their name. Microprocessors

can also be found in electronic deices!machines such as fuel in"ection systems for

automobiles# aeroplanes and een micro$aes.

The first microprocessor $as the %ntel &'' introduced in *. The &''& as not ery

po$erful + all it could do $as add and subtract & bits at a time.

The first microprocessor to ma,e a real splash in the mar,et $as the %ntel -'--#

introduced in * and incorporated into the %M PC ($hich came out around -/ +

the first pc).

0e then had the -'/-1# then the -'2-1 then the -'&-1. The naming then changed to the

Pentium# Pentium %%# Pentium %%% and Pentium & and the Celeron. 3lso 4eon and

%tanium(used in serers mostly). 3ll of these processors $ere made by %ntel $ho hae

no$ introduced a 5ual Core and a 6uad Core processor in their line of processors.

%n the meantime they no$ hae competition in the form of another ma"or company

manufacturing processor7 3M5. 3M5 calls its chips 3thlon and 5uron. 3M58s chips

are cheaper than %ntel8s. (3lso Cyrix and %M)

The microprocessor is $hat determines the generation of the computer.

Microprocessors are put onto a special soc,et on the motherboard but they are not

interchangeable# so an %ntel chip can not be replaced by an 3M5 chip unless the

motherboard itself is also changed.


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The processor is regarded as the brain of the computer as it is the part of the computer

that executes the programs. %n fact the processor is really the compute7er as it is the unit

that interprets and carries out the instructions that operate a computer. ecause of its

importance $e are going to spend some time getting to ,no$ more about it.

%t has seeral subunits but $e are concerned principally $ith the

Control unit

3rithmetic logic unit and

9egisters

Components

Control Unit

7 :e;uentially accesses and decodes program instructions

7 Coordinates the flo$ of data in and out of the 3LU# registers# 93M# storage and

input and output deices.

3rithmetic!Logic Unit

7 performs mathematical operations

7 ma,es logical comparisons

7 stores current data ! results

7

9egisters 7 a small number of ery high speed special7purpose memory units found in

the CPU capable of temporarily storing a single piece of data!instruction!address. The

register holds one unit of program instruction or data# immediately before or during

processing by the CPU. :o the register is the storage unit inside the processor. The

register is $here the data is actually stored $hile it is being processed.

9egisters are specialiMemory data register M59 + stores the current piece of data

Memory address register M39 + stores the address of the place of memory

to loo, for the next item of data needed

%nstruction register ! program counter PC + stores the current statement in the

program being executed.

3ccumulator 7 stores the results of calculations (in the 3LU)

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Processors are differentiated by >7

. their instruction set> the set of basic instructions that a particular

microprocessor can understand and execute. These are predetermined by and built

in by the manufacturer of the chip and cannot be changed.

Processors can be C%:C or 9%:C.

CISC+ complex instruction set computer > the instructions are complex i.e. a

single instruction results in seeral operations being done by the processor e.g.

MULT + load the data into the register from memory# multiply them and place the

result bac, into the appropriate register. This is at least three steps but it is

accomplished by one instruction ,no$n to the processor. C%:C computers use lessmemory space and are slo$er to execute# but they can carryout more complex

operations $ithout the interention of soft$are.

RISC+ reduced instruction set > this is a ne$er approach in $hich eery

instruction is a simple one step operation. 3 9%:C processor $ould not recogni

7 5ata manipulation + these include

o 3rithmetic operations such as add# subtract# multiply# diide# increment

and decrement

o Logical operations such as 3@5# ?9# @?T and 47?9o Compare# shift

7 Control + these include

o Testing and branching

Conditional AUMP + %B# loops

Unconditional AUMP 7 subroutine calls# returns

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7 %nput!output + these include

o 5ata transfer operations such as moe# load# store

Moing data from memory to secondary storage

Moing data bet$een registers or from register to memory

! Instruction "or#$t

=ery computer program has to be translated to machine language before it can be

executed. =ach statement in this program is called a machine code instruction.

%nstructions hae / main parts >

7 the operation code (the function that is to be done)

7 the operand (consists of the address or the data to be operated on)

The operation code tells the control unit $hat to do $ith the rest of the data8.

The exact format of the statements in the machine language ersion (ob"ect code)

of the program $ill ary depending on the type of processor $hich $ill carry out

the instruction.

=.g. of a machine code instruction

Lets8 suppose that in this processor of the 1 bits the op7code is the first & bits and

the rest of the instruction is the operand.

3n instruction may be configured in one of seeral $ays >

a) the entire machine code is the

operation!instruction. This is possible $ith instructions such as

CLC + clear

9T: + return3:L + shift left one bit

They re;uire no additional information.

Most machine code instructions hae the t$o basic parts (at least) ho$eer. There

are seeral schemes of addressing called +

' ' ' ' ' ' ' ' ' ' ' '

&


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A%%ressin& #o%es

Note that while our discussion below relate to a one addressmachine code (if the

operation needs a second operand it can be found in the accumulator); lots of

operators require 2 operands. The instruction code can therefore be a two-address

instruction in which the operand specifies where both pieces of data can be found so

that the operand is really two addresses. In this schema one address is usually in

memory and the other a register. The following list is far from exhaustie.

b) i##e%i$te $%%ressin&+ in immediate addressing the operand is not an

address# it is the actual data to be used.

This could therefore mean add '''''''''' to the contents of the

accumulator

c) %irect $%%ressin&+ in direct addressing# the operand is the address in

memory $here the data to be used is located. This means that one or more

extra access of memory is re;uired before the operation can be completed.

This could therefore mean add $hateer is stored in memory location

'''''''''' to the contents of the accumulator

d) in%irect $%%ressin&+ in indirect addressing the operand is the address of

the location $here the address of the data can be found. 9am $ill first haeto be accessed at that address to pic, up the address of the dataD then the

data location is found and that data is read into the processor.

' ' ' ' ' ' ' ' ' ' ' '

' ' ' ' ' ' ' ' ' ' ' '

' ' ' ' ' ' ' ' ' ' ' '

E


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This could mean go to '''''''''' and there you $ill find the address

of the data that is to be added to the contents of the accumulator

e) in%e'e% $%%ressin&+ in index addressing the re;uired address is found by

adding the operand to the contents of a special address register or index

register. The operand is therefore regarded as an offset from that base

address. This method is actually used to process arrays.

3ddress register

%n this case the operand '''''''''' is to be added to ''''''''' in

order to obtain the address of the actual data to be used

!ome boo"s may also mention register addressing. In this mode the the operand is

the name of the register that holds the data

3ll of this of course assumes "i'e% (en&th $%%ressin&.

:ome processors use )$ri$*(e (en&th $%%ressin&. That means that the number of bits

used for the operation code s the operand can ary from instruction to instruction.

0e8ll leae the details for our first year uniersity computer science course.

@ote that one single machine may use more than one addressing mode. %n such cases

a mechanism is needed to indicate to the processor for each instruction ho$ it should

be interpreted. ?ne $ay is to use one or more bits in the instruction code to indicatethe addressing mode

' ' ' ' ' ' ' ' ' ' ' '

' ' ' ' ' ' ' ' '

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The instruction si#e+ the number of bits or bytes in one instruction for a particular

machine. This is naturally related to the $ord si


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Y. C. Lemard

2. 3 microprocessor has / bit function codes (operators) and & bit addresses. Fo$

many different instructions can it handle and ho$ many addresses can be directly

addressedG

The number of operators range from '''''''''''' to

HI // HI &'1

The number of addresses range from '''' to HI /& HI 1

&. Using the examples aboe "ustify the need for the indirect addressing mode!scheme

E. 9esearch and ,no$ the name and purpose of at least 1 CPU registers

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?ther %mportant Processor Concepts

C$che #e#ory+ The processor is the fastest element in a computer system. ?ften it is

idly $aiting on data or instructions. Cache is one $ay to proide ready access to data for

the processor. y locating it near to or inside the processor and storing the most

fre;uently used pieces of data in it# the processor8s $ait time is reduced

The c(oc7 is a simple electronic mechanism inside the processor $hich regularly

produces a pulse of electricity used to synchroni


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uses are dedicated to one ,ind of tas,. Microprocessors hae

7 an address bus > sends addresses to and from memory

7 a data bus > sends data to and form memory

7 a control bus > carries control information from the control unit to and

from other deices

'


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%n indirect addressing# the si

08 - the processor - students version

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