MaximumPC 2005 06

46 MA XIMUMPC JUNE 2005

Q

If the two cores are on the

same die, can they communi-

cate with each other directly?

A

It depends on whose chip

you’re referring to. You might

think of Intel’s Pentium D as a

duplex house: The PD uses two

separate cores integrated into a single

CPU package. Each house has its own

kitchen, bedroom, and closets—the only

thing they share is a common wall.

While this first-generation dual-core

part is exciting, future iterations will

share components—at least where it

makes sense. To use our duplex-house

analogy, what if you wanted to move a

box from a closet in house one to a clos-

et in house two? Right now, you’d have

to walk out the front door (the bus in-

terface) of house one, onto the sidewalk

(the front-side bus), walk next door and

through the front door of house two (the

bus interface for the second core), and

find the closet. In time, CPU cores might

be able to communicate directly across

the cores (much like adding a doorway

in the common wall) and avoid using the

slow front-side bus altogether.

AMD takes a more integrated ap-

proach: The Athlon 64 X2 uses a high-

speed cross-bar interface to connect

the CPU cores via the on-die memory

controller. Unlike the Pentium D cores,

AMD’s Athlon 64 X2 cores can communi-

cate directly through this cross-bar inter-

face. Going back to our duplex analogy,

this is like walking onto a shared porch to

go next door, versus walking down one

sidewalk and up the other.

Q

Multitasking is cool, but if dual

core doesn’t benefit my cur-

rent applications, why don’t

Intel and AMD just continue

making ever higher-clocked single-core

processors?

A

AMD and Intel both recognize

the shortcomings of dual-core

processors with unoptimized

software, so both companies

will continue pushing their highest-

clocked chips to gamers and other

people who don’t give a damn about the

benefits of multitasking. Both companies

also realize, however, that throttling-

up clock speeds delivers diminishing

returns: Faster processors consume

more power and generate more heat,

which offset the benefits of higher clock

speeds. The most public

demonstration of this change

in philosophy occurred last

year, when Intel surprised the

industry by killing its plans to

introduce a 4GHz Pentium 4.

Both companies can still

eke out more performance the

old-fashioned way, but there’s

no doubt that the future lies

in CPUs with two—or more—

cores.

Q

Why doesn’t a dual-

core chip consume

as much power as a

higher-clocked P4,

or generate twice as much

heat?

A

Intel says a dual-

core processor is a

shade or two below

the heat-generation

and power-consumption lev-

els of its fastest single-core

processors. The company

was able to keep power and

thermals under control by

borrowing some tricks from its mobile

cores, and by using enhanced sleep

states to keep the CPUs cooler.

Q

Should I care about dual-core

processors if all I want to do is

play games?

A

Well, it depends on what you

mean by “play games.” If you’re

building a machine that will

be dedicated to just gaming,

then the fastest single-core processor

available is the way to go; at least until

more games are multi-threaded. But if

you ever want to transcode a video while

simultaneously browsing the net or

working in Photoshop , dual core makes a

lot of sense, especially because so many

A-list games rely heavily on your video-

card for their effects. You might give up

a few frames per second in gaming with

a dual-core system, but you’ll get a far

more responsive PC for everything else

you do.

Q

What will be the specs of

Intel’s first consumer dual-

core processors?

A

Intel’s desktop dual cores will

be introduced in two breeds:

The Pentium D (PD) and the

Pentium Extreme Edition

(PEE— tee-hee ). Both are based on the

90nm Prescott core that Intel introduced

in early 2004, both run on the 800MHz

front-side bus, and both include 1MB of

L2 cache. The key differentiator between

the Extreme Edition and the Pentium

D is the absence of Hyper-Threading

on the latter part (Intel simply turns off

that function). A PD will show up in a

machine as two CPUs, while the PEE

will show up as four procs (with two

of those being Hyper-Threaded virtual

processors). If you’re wondering why

the Extreme Edition doesn’t run on a

1066MHz front-side bus, it’s because

Intel says it can’t execute dual core on a

faster front-side bus on today’s mobos

without adding electrical noise. In order

to run at 1066MHz, the motherboards

would require additional layers, which

would increase manufacturing costs. The

company hasn’t ruled out a faster FSB

in the future, but it’s capped at 800MHz

for now. Both cores are hooked up to the

With the Pentium Extreme Edition, your task

manager will glow with the light of four processors

(see the four graphs under CPU Usage History),

something you could only achieve previously with a

dual Hyper-Threaded Xeon or a real four-proc box.