Elenco Electronics MO-1251 Manual do Utilizador descarregar pdf (Página 77)

100

TRANSPUTER

continued from

page 77

Divide

and

conquer

The idea

is to

divide and con-

quer; let's

illustrate with

an anal-

ogy.

If,

for example, you

find that

your

secretary is not

getting her

work done

because of constant

telephone interruptions,

you

hire

a receptionist

and divide the

workload

between the

two, there-

by improving

productivity.

a similar manner.

a comput-

er can

divide and distribute

its

workload

by offloading portions

of it

to other processors.

Whereas

dedicated

hardware

-disk con-

trollers and video

adapters,

for

example-

improve

system per-

formance

doing some

of the

CPU's work, those

types of con-

trollers typically

differ from

gen-

eral- purpose

processors

in that

they require

step

-by

-step instruc-

tions from

the CPU about

how

operate.

contrast,

a processor gets

its orders

directly from

the

soft-

ware application

without

involv-

ing the

CPU at all. That

leaves the

CPU free

to do other

things, and

thereby

increases overall

produc-

tivity. In

addition, a general

-pur-

pose processor

can be adapted

a number

tasks, whereas

the

typical hardware

controller

can

only

do one

thing, albeit very

well.

Basically, there are two dif-

ferent types of

processors:

coprocessors and parallel

pro-

cessors, although the distinction

between them

times hazy.

Strictly speaking, a coprocessor

is a processor dedicated to one

task and one task alone -like the

receptionist

the example. Par-

allel processors, on the other

hand, can function in different

situations.

In what follows, well discuss

several parallel and coprocessing

products for the IBM family. Keep

in mind, however, that compara-

ble products for

the

Apple

and

other

systems

are available.

Number crunching

The most popular and best

known

coprocessors are the

math coprocessors from Intel:

the 8087, 80287, and the 80387.

Those IC's work in conjunction

with

the 8088/86,

80286,

and

80386 CPU's,

respectively,

and

usually plug directly

into

socket

on the PC's

motherboard.

As the name suggests,

math

coprocessor does

nothing

but

mathematical calculations

-a

task that a general-

purpose

mi-

croprocessor

is very slow at.

The

chip

doesn't

do windows

and it

can't read a disk -but

it can mul-

tiply two

numbers as much

100 times

faster than a CPU

itself.

lb give you

an idea of how

math

coprocessor can improve

performance, consider the

math -

intensive CAD program,

Auto -

CAD.

Without a math

coprocessor, even simple

Auto -

CAD drawings can

take several

minutes to compute for display

using just the CPU as

a number

cruncher.

However,

when a math

coprocessor is installed,

Auto -

CAD recognizes

its

presence

and

diverts all

math routines to

rather

than

forcing them

through the CPU. Then,

while

the coprocessor

is busy munch-

ing

mantissas,

the CPU is analyz-

ing the results and placing them

on the screen.

The outcome of

that

partnership is a tenfold

in-

crease in speed.

You want to

windows?

If it's screen performance you

want, there are coprocessors

for

that, too.

Popular IC's include

'I xas Instruments 34010,

Intel's

82786, and others

from Hitachi,

National Semiconductor,

and

others. Like the

math

coprocessors

discussed above,

video coprocessors are optimized

for a single task:

manipulating

graphics on a video screen. They

can't access a disk drive or read

keyboard, but they

sure

can

move pixels around!

Unlike the simple

interface be-

tween the microprocessor and

the

math coprocessor, video

coprocessors usually

require a

good deal of support

circuitry.

Commercial products include

the Pepper 1600 from Number

Nine Computer and the Ultra

2000 CAD from INI Computer

Systems.

Unlike typical

IBM -style video

controllers

(Hercules,

EGA.

etc.),

those

video

adapters

use

video

coprocessor

IC's that

receive

dis-

play

instructions

directly

from

applications

software.

In that

sit-

uation. the

CPU

is relegated

sim-

ply to coordinating

screen

opera-

tions

with keyboard

input,

disk

access,

and other

housekeeping

system

functions.

Parallel

processors

Parallel

processors

are

versatile

than

dedicated

coprocessors

because

they can

programmed

to do more

than one

thing,

be it number

crunching,

video graphics,

or just

plain sys-

tem

routines.

Like a coprocessor,

a parallel

processor works

alongside

the

main CPU and

receives

its in-

structions

from the software

ap-

plication rather

than from

the

CPU. Generally,

each parallel

pro-

cessor is an

island unto

itself. It

is assigned

a specific task.

it does

it, and then it

waits for another

assignment.

A crude analogy

to parallel

pro-

cessing is

a local -area

network

(LAN). in which information

accessed by an

individual

node

from a shared data

bank, and

then

processed according

to the

user's needs. Then the

results

are

returned to the

data bank so

that

others

may make use of

it.

Parallel processors

handle

things

on a

more basic

level.

Whereas the

LAN may have

than one application

running on

the

network, with each

user

using

a different piece

of soft-

ware, the

parallel processor

driven by one

all- encompassing

application that

takes total, con-

trol of each processor.

The transputer

An increasingly

popular paral-

lel processor

for PC applications

is called a transputer,

an acro-

nym

derived

from TRANSistor

comPUTER. The term

was coined

INMOS Corp. of Bristol,

En-

gland, (the same

company

that

makes the

DAC used in

most

VGA adapters);

it basically

means a computer

on a chip.

In fact, INMOS makes two

transputers: the

T414 and the

T800. As shown

in Fig. 1. the

T414 is a 32 -bit CPU with

2K of

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