Elenco Electronics MO-1251 Manual do Utilizador descarregar pdf (Página 71)

COMPUI

COMPUTERDIGEST

A PC run

circles

oround

o Cray?

Despite advances in micro-

processor technology,

the

single -CPU architecture

of the

personal computer limits

the

maximum rate

at which data can

be processed. There is

just so

much data

you can cram through

a processor

in a given amount of

time.

While faster clock rates provide

some relief, all other things being

equal, performance only in-

creases linearly with clock

speed.

A 16 -MHz

system,

for

example,

would

be twice as fast as an 8-

MHz

system. However, we are fast

approaching the speed limit of

our present

technology.

Wider

data buses provide an-

other avenue for improvement.

Dur'ng the past decade,

the

data

buses of common

PC's have dou-

bled

in width twice, from the 8-

bit

buses of the Z80 and the

8088, to the 16

-bit

buses

of the

80286

and 68020, to the

32

-bit

TJ BYERS

buses of the

80386 and the

68030.

However, those wide new

buses

are straining conventional

hardware

and software

tech-

niques

to the limit.

The

point is that we're reach-

ing the attainable limit

of perfor-

mance

improvement by

increas-

ing raw

CPU speed. Fortunately,

however,

there is

hope. To in-

crease performance,

savvy PC

users

are adding dedicated

coprocessors

and general -pur-

pose parallel

processors

to their

systems -processors

that are de-

signed to increase

performance

by assuming

at least

partial re-

sponsibility for

the processing

workload.

In fact,

given enough process-

ing help, there is no limit

to

what

a PC can do. For about the price

of a workstation,

a single PC can

run circles around

a

mighty

Cray

1S

supercomputer.

continued on page 83

EDITOR'S

WORK-

BENCH

Presentation

Manager

5/2 Standard

Edition Ver-

sion 1.1 (Presentation

Man-

ager,

or PM for

short) was

released

on

Halloween, 1988.

It's

not

something you want

to rush

out

and buy,

because there's

not

much you

can do with it.

But it is

something

you want

to get a

hands -on

look at, because

it's a

harbinger

of the future.

JEFF

HOLTZMAN

The long -awaited

graphical

in-

terface for

OS

/2 is:

Big

(8MB

of hard disk space is

required)

Hungry (3MB RAM minimum)

Slow on anything

but a fast

286

or 386

Y...r.r uve

CVO ..®®rtIrrt.mea

r

ewea

Doe Wyk 1....rrMow.

.1.

an w1./.

yr.w

D

rf..S.1Mrtr1le Mel rr Ile

rlam

r....

continued on page 78

Build an

intelligent

cable

tester

for

only

$25!

JIM

BARBARELLO

/ single

fault in

a printer or

modem cable can disable the

device

just when you need it

most. A

cable fault is not a prob-

lem if you're

a cable manufac-

turer, because

you can use your

sophisticated (and expensive)

ca-

ble tester

to troubleshoot the ca-

ble.

The problem is that most

of

us can't afford

that type of equip-

ment. There is,

however, a simple

and inexpensive

alternative. If

you own

a

PC

and have about

$25

in

spare change, you can build

your own multi -line

cable tester.

Our tester connects to your

PC's

printer

port

and allows you

to

test any cable with

as

many

as

24 active lines.

The tester works

by performing

a continuity

check

on the 576

possible interconnec-

tions; a complete

test takes only

about ten

seconds. The tester

uses

inexpensive, readily avail-

able components,

is built on a

solderless

breadboard (so no PC

board is required),

and is con-

trolled by

a simple BASIC pro-

gram,

which you're free

to

modify

or enhance.

Multiplexing

lb

understand how the cable

tester works, let's review

the con-

cept of multiplexing.

Consider

the

circuit shown in Fig. 1. The

two rotary

switches are ganged,

so

both sections change

simulta-

neously.

In each position a dif-

ferent

device glows: LED1, LED2,

or LMP1.

However, if we rotate the

continued

on

page

80

77

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