MaximumPC 2004 08

I

f you’re not confused enough by the

myriad CPU offerings from AMD

and Intel, here’s one more change to

push you over the edge: AMD’s Socket

939 will likely be the standard bearer of

AMD’s performance-oriented CPUs for

the foreseeable future. Hopefully, fans of

AMD haven’t been caught off guard by the

news; AMD has always indicated its plans

to consolidate around the Socket 939.

To get you up to speed, we put

together a short brief on the new socket—

including AMD's plans for the older

sockets.

What’s the key difference between Socket 939

and 940?

Socket 939 may look nearly the same as

Socket 940, but there’s one key difference:

Socket 939 CPUs don’t require expensive

and hard-to-find registered DIMMs to

function. Socket 940 CPUs (which were

really just Opteron server CPUs) could

only work with registered RAM.

I noticed that AMD has introduced Socket 939

CPUs for both the FX and the normal A64 series.

I thought they were different.

One aspect we appreciate about Socket

939 is that it finally brings some much

needed harmony back to the AMD

universe, something that has been

missing since its 64-bit CPUs came out.

In the old days, you could buy a Socket

A motherboard and choose between

a Duron or Athlon XP CPU. Intel’s

world was the same; you could pick a

motherboard that would allow you to

buy a low-budget Celeron now and plan

for a faster Pentium 4 later. This didn’t

work in the Athlon 64 world because the

CPUs used different memory controllers.

Athlon 64 memory controllers were

single channel, while the Athlon 64 FX

was dual channel. If you bought a Socket

754 motherboard and Athlon 64 3200+,

for example, you could never upgrade to

an Athlon 64 FX. In the new Socket 939

world, you can.

If both Socket 939 CPUs have the

same memory controllers, what’s

the difference between an FX and a

normal A64?

The main difference right now

is cache. With the new CPUs

that AMD has introduced, the

Athlon 64 3800+ will receive

512KB of L2 cache, while the FX

will remain at 1MB.

I thought Athlon 64s already had

512KB of cache?

Yes. AMD actually has two

cache sizes in its older Socket

754 Athlon 64s. The Athlon 64

3400+ and the new 3700+, for

example, have 1MB of L2 while

the old Athlon 64 2800+ has

just 512KB of cache. Making

things even more confusing, some

versions of the Athlon 64 have the

same speed rating but different

clock speeds and cache sizes, like

the Athlon 64 3200+. The same “3200+”

is available as either a 2GHz CPU with

1MB of L2 cache or 2.2GHz CPU with

512MB of L2 cache.

What happens to the older interfaces?

When we spoke to AMD officials, we were

told that Socket 754 will continue to be

supported. Rumors have also indicated

that AMD may actually introduce a 32-

bit only version of a CPU in Socket 754.

Socket 940, however, isn’t being treated

similarly. Backpedaling on previous

pledges that it would support Socket 940

through the year with parallel launches

(the FX-55 version of the Athlon 64 FX

was supposed to ship in both Socket

939 and Socket 940 versions), AMD now

says the support will only come through

Opteron upgrades. Because Socket 940

will still be the home for Opteron, Athlon

64 FX users will theoretically be able to

upgrade to the next spin of the Opteron.

But, umm, Opteron comes out in slower cycles.

Doesn’t that mean FX users get screwed?

Well, yes, but at least the Opteron is

cheaper. An Opteron 148 at 2.2GHz costs

about $400; the 2.2GHz FX-51 still costs

about $700. But we have to admit that we

are a little disturbed that AMD appears to

be dismissing its previous pledge. We’re

hoping the company reconsiders its

support for Socket 940.

They look nearly the same, but Socket

940 (top) and Socket 939 (below) are most

definitely incompatible.

In tHe LaB A behind-the-scenes look at Maximum PC testing

SoCKet  EXPoseD

The big news: AMD is rapidly dismissing socket 940 for

Athlon 64 CPUs

 MAXIMUMPC AUGUST 2004

Can you tell which of these is Socket 939?

DARE TO COMPARE: ATHLON 64 SOCKETS

Old New Old New

CPU Athlon 64 FX 53 Athlon 64 FX 53 Athlon 64 3700+ Athlon 64 3800+

Clock speed 2.4GHz 2.4GHz 2.4GHz 2.4GHz

Interface Socket 940 Socket 939 Socket 754 Socket 939

Memory controller dual / 128-bit dual / 128-bit Single / 64-bit dual / 128-bit

Type of RAM Registered Unbuffered Unbuffered Unbuffered

L2 cache 1MB 1MB 1MB 512KB

64-bit support? Yes Yes Yes Yes