MaximumPC 2006 12

50 MAXIMUMPC DECEMBER 2006

his hands and knees looking for naturally

occurring specimens.

QMy Pentium Extreme Edition shows

up as four CPUs in the Task Manager. Is

that the same as a quad core?

ANo. The NetBurst-based PEE840,

PEE955, and PEE965 all feature dual-core

CPUs with support for Hyper-Threading,

which turns each single core into a virtual

dual-core CPU. While Hyper-Threading works

well enough, it’s in no way comparable to a

quad-core processor. Intel doesn’t offer HT on

any of its current Core-based processors—the

company says HT cost transistors that were

better spent elsewhere right now—but it hasn’t

ruled out the return of that technology.

Q What about front-side bus per-

formance? Why doesn’t the quad core

have a 1,333MHz FSB like the Xeon

5100 does today?

AUnlike AMD, which connects all of its

cores and CPUs using a direct chip-to-chip

architecture, Intel is currently wed to its

shared-bus topology. Remember the bridge

in our island analogy? That’s the front-side

bus, and in order to move from one island

(die) to the other, you have to travel that

bridge all the way to the mainland before

making your way back to the other island.

And that bridge is congested with all kinds

of traffi c that can affect travel time.

Intel claims that an analysis of the bus

traffi c under heavy loads using today’s appli-

cations indicates that we’re not even close to

saturating the FSB. Is that true? It’s hard to

say. Intel engineers do admit that it’s possible

to saturate the bus, but that you’d have to

write code specifi cally to do that. By foregoing

the 1,333MHz bus for this generation, Intel is

putting its architecture where its mouth is. Still,

no one at Intel has ruled out a move to a faster

front-side bus in the future, which suggests

that the company thinks traffi c might need to

be addressed at some point.

Q If the QX6800 is two Core 2 CPUs,

does that mean it has 8MB of L2 cache?

ATechnically, yes. Because the

QX6800 is essentially two Core 2 Duo E6700s

welded together, the cache remains the same

per die (64KB of L1 cache and 4MB of “smart”

L2 cache), for a total of 8MB of L2 cache

among the four cores. Remember, however,

that each set of two cores is on its own island.

The two cores on one island cannot share

cache with the two cores on the other.

The cache is still smart, though, which

means the two cores on one island can share

their 4MB dynamically. If one core is idle, the

other core can use all 4MB of the shared L2

cache. Both cores also communicate across

the cache—each core knows how much of the

cache the other is accessing. In a more tra-

ditional design, where each CPU core has its

own dedicated cache, if core 1 and core 2 are

working on the same data and core 1 needs

something that’s already in core 2’s L2 cache,

it can’t just grab it, it has to go out to main

memory to get it.

So while communication between the

two dies has to happen via the comparatively

slow front-side bus, communication within the

individual dies will enjoy all the benefi ts of the

original Core 2 Duo. This helps supports Intel’s

claim that the FSB design isn’t a problem.

QWill quad core work in my LGA775

motherboard?

AIf you listened to our advice and held

off buying an LGA775 mobo until it was

certifi ed to run with Core 2 processors, you

have a very good chance of it working with

a simple BIOS upgrade. That makes us

happy because, for the fi rst time in a long

time, Intel’s CPU and chipset/mobo folks

seem to be talking to one another.

QHow can I ensure that the mother-

board I buy supports quad-core CPUs?

AThe safest way is to check with the

vendor. If the website or package says the

mobo is quad-core ready, the vendor is on

the hook to support it. Still, some moth-

erboards that are capable of supporting

quad core require a BIOS update before

they will boot a quad. If you don’t have

access to another LGA775 processor to

use when fl ashing the BIOS, most vendors

will either fl ash the board for you before

they ship it out or exchange the board for

one with an updated BIOS.

QWhy is Intel offering its quad core

and dual core at the same price? Wouldn’t

it make sense to charge more for quad?

AThe procs are priced as such

because in today’s computing climate, each

offers advantages, but neither can claim

outright superiority. The dual-core Core 2

It’s a twofer! For the price of a

single X6800, you get two of those

dual-core CPUs in a single package,

for quad computing.

Quad Power!Quad Power!Quad Power!