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AMD's Athlon 64 3800+ and FX-53 processors


Socket 939 at last
— 12:01 AM on June 1, 2004

I KNOW FOR A FACT that more than one PC enthusiast has been eyeing the Athlon 64 with anticipation, but has been paralyzed by the Osborne Effect field surrounding the Socket 754 versions of the processor. You see, back when the Athlon 64 was launched, AMD promised the world—right out of the gate—a new, 939-pin socket that would bring dual-channel memory to every Athlon 64. Since then, the single-channel versions of the Athlon 64 have been handing out beatings to the Pentium 4 in most gaming benchmarks. Enthusiasts have been torn between grabbing for the extra performance now or holding out for the big prize, the Socket 939 versions of the Athlon 64.

Meanwhile, the dual-channel Athlon 64 variants, the FX-51 and FX-53, have been absolutely laying waste to our entire benchmark suite. Those chips are expensive, however, and have a few liabilities. The Athlon 64 FX processors inherit their dual-channel memory capabilities from the Opteron line, and they slide into the same 940-pin socket as the Opteron. Socket 940 processors require registered DIMMs, which are a little odd, a little pricey, and have slightly higher memory access latencies than regular ol' unbuffered DIMMs. Also, the motherboard options for the Athlon 64 FX have been adequate, but not particularly spectacular, varied, or affordable.

Socket 939 promises to address these problems by allowing motherboard manufacturers to make dual-channel DDR400 motherboards with cheaper four-layer PCBs, and by allowing the use of unbuffered DIMMs. Also, AMD has officially blessed the use of a 5X multiplier on the HyperTransport links connecting Socket 939 processors to the rest of the system, raising the peak effective bandwidth for this link to 8.0GB/s.

Today, AMD lifts the curtains on four new processors, three of them for Socket 939. We've had two of those CPUs, the Athlon 64 3800+ and Athlon 64 FX-53 (939-pin edition), in Damage Labs for review. Naturally, we've run them through our gauntlet of benchmarks and compared them to nearly 20 different competing processors. Keep reading to find out whether Socket 939 lives up to its promise.

Socket 939 up close
Both of the new AMD CPUs we have for review run at 2.4GHz and drop into a 939-pin socket. In fact, the main difference between the Athlon 64 3800+ and Athlon 64 FX-53 is 512K of on-chip cache. Like its 940-pin counterpart, the Socket 939 Athlon 64 FX has 1MB of L2 cache on chip, while the Athlon 64 3800+ has 512K of L2 cache. Before we get worked into a fit of hysterics trying to explain AMD's model number schemes, let's have a look one of the new Socket 939 chips.


The Athlon 64 3800+


The 939-pin underside of the Athlon 64 3800+


The 940-pin belly of the Opteron 150

The 939-pin Athlon 64 doesn't look wildly different from its predecessors, and at first glance, one might think that the only difference between the 940- and 939-pin chips was that single missing pin at the lower left corner of the picture above. However, a closer look reveals that AMD has moved the location of some of the "gaps" in the pin configuration where no pins exist. Socket 939 is well and truly incompatible with Socket 940, so there's no hope of running a 939-pin chip in a 940-pin motherboard. The worlds of the Athlon and the Opteron will be a little more separate from now on.