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The processors
The systems we're looking at today are based on x86 CPUs from AMD and Intel, the Opteron and Xeon, respectively.


$1176 worth of processors—at least back when we bought 'em

If you're familiar with Pentium 4 processors, then Xeons ought to look mighty familiar. Today's Xeon is essentially the same chip as the Pentium 4, sold under a different name. It has the same Netburst architecture as the Pentium 4, and it's made on the same 0.13-micron fab process as the Pentium 4. Unlike the P4, however, Xeons are capable of running in multi-processor configurations. Xeons also come in a slightly larger package than the P4, with 604 pins to the Pentium 4's current 478. The Xeon model we're testing today is the 2.66GHz version with 512K of on-chip L2 cache and a 533MHz front-side bus.

At the time when we started work on this article, the Xeon 2.66GHz was exactly the same price—$294 a pop, American money—as the Opteron 240 to which we'll be comparing it. Since then, Intel has moved to counter AMD's Opteron with some aggressive moves, including cutting prices, adding a 1MB L3 cache to some models, and moving to an 800MHz front-side bus with dual channels of DDR400 memory. We invited Intel to participate in our comparison with newer Xeon models, but it elected not to do so. Newer Xeon models (and motherboards to support them) are just now becoming available, so you may not see too many pre-assembled workstation rigs based on them just yet, anyhow.


The Xeon's 604-pin package

AMD's Opteron chip may not be as familiar to most folks as the Xeon, because the desktop variant of the Opteron hasn't yet hit store shelves. This new chip, based on AMD's K8 "Sledgehammer" architecture, brings a number of enhancements over the K7 architecture in the Athlons XP and MP. The Opteron packs an on-chip, dual-channel memory controller to reduce memory access latencies and allow for better performance scaling as the number of processors in a system rises. Also, the Opteron supports Intel's SSE2 instruction set (in addition to AMD's own 3DNow!), enabling accelerated SIMD computations with double-precision floating point datatypes. Many workstation apps use SSE2, especially for 3D rendering, so this addition is important. The Opteron's larger, 1MB L2 cache won't hurt, either. On the speed front, AMD has lengthened the K8's pipeline to 12 stages (from the K7's 10) and moved to a new, 0.13-micron silicon-on-insulator fabrication process in order to help the chip run faster and cooler.

Finally and perhaps most importantly, the Opteron is a true 64-bit processor. Through the use of AMD's 64-bit extensions to the x86 instruction set architecture (ISA), the Opteron can run 64-bit operating systems and applications. This 64-bit capability breaks several barriers, including the ability to address more than 4GB of memory directly. In the workstation market, the x86 PC's traditional 4GB memory barrier can be a crippling problem, so AMD probably won't have to work too hard to make the case for 64-bit computing here. Operating systems and applications will have to be recompiled in order to support AMD64, but that work is already happening in both the Windows and Linux universes. The AMD64 ISA also includes more registers, or temporary on-chip storage slots, than the 32-bit x86 ISA. Recompiled applications may show substantial performance gains on AMD64 even if they can't take advantage of AMD64's expanded memory address space, because the chip won't have to resort to cache accesses as often.

We haven't yet tested the Opteron with 64-bit software, but you'll see shortly that it performs quite well running 32-bit code. AMD's 64-bit extensions haven't diminished the K8's 32-bit performance.


The Opteron's imposing 940-pin underbelly