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FX

PHOTOGRAPHY BY SAMANTHA BERG AND MARK MADEO

Q

What’s the difference between Quad

FX and Intel’s quad-core Core 2

Extreme QX6700?

A

The main difference is in the

way each company packages

its four execution cores. Intel

essentially packs a pair of

dual-core CPUs into a single CPU pack-

age. AMD’s dual-core CPUs are larger,

so two won’t fi t in a single CPU pack-

age. Instead, AMD takes two dual-core

processors and puts them on the same

motherboard. In other words, Intel’s quad

core describes the CPU, while AMD’s

quad core describes the PC.

In the end, however, the results are

similar. Pull up the Task Manager in

Windows XP or Vista and you’ll see four

green graphs—one for each execution

core. Your applications have access to

four discrete CPUs.

Quad FX refers to the entire platform

of motherboard and CPU; the processors

themselves are called Athlon 64 FX-70,

FX-72, and FX-74, which clock in at

2.6GHz, 2.8GHz, and 3GHz, respectively.

Each dual-core processor features 1MB

of L2 cache per core and is almost identi-

cal to its Socket AM2 sibling.

Q

Isn’t calling Quad FX “quad” a

misrepresentation?

A

If you defi ne quad as a four-

core CPU, then yeah, AMD’s

moniker is misleading. If you

defi ne quad as four cores in a

PC, AMD is technically accurate, although

we’ll say that this is probably the loosest

way ever to defi ne a quad-core machine.

To CPU-architecture snobs who think

Intel’s trick of joining two dual-core CPUs

together is just a hack, the Quad FX plat-

form rates as an even greater affront.

Q

Why doesn’t AMD just introduce

its quad-core single-socket

processors sooner?

A

While Intel took the shortcut

to quad cores by mounting

two 65nm dual cores on a

single CPU package, AMD

is handcuffed by its current 90nm pro-

cess. AMD simply can’t create a mul-

tichip module like Intel’s because the

sheer physical size and the thermal and

electrical constraints of its 90nm-based

dual-core CPUs make it impossible.

AMD is stuck until it gets its own 65nm

process off the ground. Adding to the

dilemma is the fact that AMD has signif-

icantly fewer engineering and assembly

resources than Intel. While Intel boasts

15 fab lines, AMD owns just two and

contracts out for its third.

Q

What are the advantages of dual-

processor motherboards?

A

Dual-processor mobos are fi rmly

in the realm of the workstation

class, and generally, they’re

built to the higher specifi cations

and standards of mission-critical work. In

the Quad FX platform, AMD has a couple

advantages over the single-socket Intel

boxes. Because there’s a memory control-

ler embedded in each Athlon 64 proc, a

Quad FX box with two CPUs gets two

memory controllers, which can offer a per-

formance boost in certain memory-inten-

sive situations. A dual-processor rig will

also offer an upgrade advantage you won’t

get with a single-CPU box. Come this sum-

mer or fall, for example, you should be able

to upgrade your machine to two quad-core

CPUs and have yourself a nice octo-core

rig. If you want eight cores in a PC with a

single CPU socket, you’ll have to wait until

at least 2008. Even then, it’s quite possible

the octo core won’t work in your single-

proc board—chipset architectures will likely

change between now and then.

Q

What are the disadvantages of

Quad FX?

A

The main disadvantage is price,

since you will have to purchase

both a more-expensive mother-

board and two CPUs. There

are also greater power requirements for two

CPUs, which in turn leads to additional heat

that must be addressed.

For example, the quad Core 2 Extreme

QX6700 has a 130-watt thermal design

profi le (TDP). Each Athlon 64 FX-74 has a

TDP of 125 watts, for a total of 250 watts.

Even though Intel and AMD defi ne TDP

differently, the Quad FX platform will be

hotter and use more power than a single-

processor rig. And while you might get

away with a cheapo power supply for a

single-processor PC, using anything less

than a high-quality, high-output PSU on

the Quad FX platform is asking for trouble.

Oh, and don’t forget to kiss your mid-

tower case goodbye. To accommodate a

dual-CPU rig’s larger mobo and hefty PSU,

and the greater thermal loads of two procs,

you’ll need a big, fat full-tower case.

Let’s not forget the memory either.

To get the best memory performance

from a Quad FX machine, you’ll have to

populate two channels per CPU, which

means you’ll have to fi ll four DIMM slots

instead of the two you’d fi ll for a single-

processor machine.

Q

How different are the Quad FX Athlon

64 FX CPUs than the Socket AM2 ver-

sions? Can you use Opteron CPUs with

a Quad FX platform?

A

The Quad FX and AM2 CPUs are

almost identical beneath their

heat spreaders, but the physical

CPU packages are totally differ-

ent. The Athlon 64 FX-62 fi ts into a single-

processor Socket AM2 board using a tradi-

tional pin-grid array package. The new

Athlon 64 FX-70, FX-72, and FX-74 use

Socket 1207, which the Opteron also uses.

Socket 1207 is a land-grid array that does

away with the pins in the CPU, à la Intel’s

Socket 775. Like the 775, the 1207’s pins

are embedded in the motherboard and dig

into the grid on the bottom of the CPU for

better and more reliable contact.

The Quad FX and AM2 cores them-

selves are almost identical. Both are 90nm

and boast 64-bit support, NX protection,

and hardware-virtualization support. The

only real difference between the two cores is

in their HyperTransport implementation. All

desktop Athlon 64s, even the original FX-51

that was based on the Opteron, sport only

one HyperTransport link. On the Athlon 64

FX-70 series, however, two HyperTransport

links are active. One connects the CPU and

chipset and the second connects the CPUs

with each other. The second HT link likely

accounts for the slightly larger die area of the

70 series over the 60 series.

Unfortunately, you cannot use Opteron

CPUs in a Quad FX motherboard, nor can

you run Athlon 64 FX-70 series CPUs in an

Opteron board.

Q

Does this mean the FX will no longer

be supported for Socket AM2 boards?

Is AM2 going to die?

A

AMD insists the Quad FX is

only for uber-enthusiasts and

that it will continue to fully sup-

port the AM2 platform. The

company never discusses its future prod-

ucts, but it did say that you will absolutely

be able to buy a quad-core processor for

Socket AM2 this year. The company won’t

say, however, whether FX-labeled CPUs

What We Know About Quad FXWhat We Know About Quad FX