Intel Finally Gets 64-Bit Xeon MPs Out the Door

by Timothy Prickett Morgan

Chip maker Intel last week finally rounded out its X86 product line with full 64-bit memory and processing capabilities as it launched the "Potomac" and "Cranford" variants of the Xeon MP processors. The Xeon MP chips are the most sophisticated X86 processors that Intel makes, and they are used in machines that have four or more processors in a single system image.

Intel's "Prescott" Pentium 4 and "Nocona" Xeon DP processors, which are used in uniprocessor and two-way workstations or servers, have been shipping with 64-bit main memory support since last summer. The Nocona's were announced in June 2004, and they implement 64-bit memory support that is compatible with the 64-bit memory extensions that Advanced Micro Devices created for its Opteron processors. Intel was trumpeting the fact that its EM64T memory extensions "top-off" its 64-bit server platforms now that Potomac and Cranford are available, and were a fitting launch to commemorate the 10th anniversary of Intel's getting into the server business with server-specific processors. These are very fast processors, to be sure, particularly for applications that require lost of cache memory. But they do not entirely blunt the advantages of the Opteron line, which in a few months will have dual-core versions as well as 64-bit memory support, and nor do they make it any easier for Intel to differentiate the Xeons from the 64-bit Itaniums, which have their own EPIC instruction set that is distinct and basically incompatible with the X86 architecture. (To be fair, there is an X86 execution environment in the Itanium, but it wastes half of the processing power of the Itanium, so it is not very practical for production use.)

The two 64-bit Xeons are distinct in a way that all past server chips from Intel have been. The company is offering two versions of the chip with different caches, different clock speeds, and different prices. Both chips plug into the "Truland" server platforms, which are four-way servers based on Intel's own "Twin Castle" E8500 chipset. According to Alan Priestley, strategic marketing manager for Intel in the UK, the E8500 is pretty much the only game in town other than IBM's "Hurricane" XA-64e chipset. The ServerWorks unit of Broadcom has not ported its 32-bit "Grand Champion" chipset to the 64-bit variants of Xeon.

The Cranford chip is being billed as the "value" Xeon MP platform. It is available with 1 MB of L2 cache memory and running at 3.16 GHz and 3.66 GHz. That L2 cache size is pretty small, as small as the original Nocona 64-bit Xeon DP processors announced last year. And those clock speeds are not a lot higher than the 32-bit "Gallatin" Xeon MPs they replace, which ran at 3 GHz when they were kicked up a notch about a year ago, but which offered 4 MB of L2 cache memory. A little more clock speed and a lot less cache is not a good option for a lot of workloads. However, for many workloads and for a cheaper line of 64-bit, four-way servers (something that Dell certainly wants and the other server makers, who have 64-bit Itanium or RISC/Unix platforms, have to cope with because Dell wants it), the Cranford chip is just what is needed. Why? Because is it cheap. A 3.16 GHz Cranford chip costs $722, and the 3.66 GHz version costs $963. (That's for 1,000-unit quantities, of course.) Those prices are just a little bit higher than what Intel has been charging for 64-bit Xeon DP processors. Up until now, Xeon MPs have commanded a much higher premium.

And that is what the Potomac "performance" Xeon MP is all about. For customers who need big L2 and L3 caches on their server processors, Potomac is essentially a 64-bit crank on the existing Gallatins. The Potomac chips come in three flavors: a 2.83 GHz version with 4 MB of L3 cache, a 3 GHz version with 8 MB of L3 cache, and a 3.33 GHz version with 8 MB of L3 cache. That's a little bit more clock performance and twice the cache of the fastest 32-bit Gallatins, which came in 2.2 GHz/2 MB cache, 2.7 GHz/ 2 MB cache, and 3 GHz/ 4 MB cache versions. The Potomac processors cost exactly the same as these Gallatins, too. That's $3,692 for the 3.33 GHz/8 MB cache Potomac, $1,980 for the 3 GHz/8 MB cache Potomac, and $1,177 for the 2.83 GHz/ 4 MB cache version.

Customers looking at Potomac and Cranford want to know two things: How much more performance will the Truland platform have compared to Gallatin-based systems, and what is the performance difference between Cranford and Potomac within the Truland designs. Intel has run a series of benchmarks on the new Truland platform, which includes dual 667 MHz frontside buses (which packs 10.6 GB/sec of bandwidth, three times that of the Gallatin platform), support for 400 MHz DDR2 main memory (with 64-bit addressing, obviously), and other improvements like PCI-Express peripherals. With all of that extra stuff, some workloads that are cache and bandwidth sensitive, like the SPECfr_rate test and the Linpack benchmark, are seeing performance increases by 65 percent and 57 percent, respectively. The TPC-C benchmark test, however, only saw an increase of about 15 percent (possibly because the 64-bit versions of Windows and SQL Server are not yet available) in moving from the Gallatin to the Potomac platform. Performance on the SAP ERP suite only increases 7 percent.

According to Priestley, Intel's tests show that a Potomac 3.33 GHz/8 MB chip will best a Cranford 3.66 GHz/1 MB chip by 40 percent on the SPECfp_rate test and by 23 percent on the SPECint_rate tests on four-way servers using the same E8500 chipset. Potomac still offers a considerable performance benefit, but Cranford is the clear winner (at least as far as these tests are concerned) in terms of bang for the buck. Plenty of customers will sacrifice a lot of performance to get a lot less expensive server if they need the big main memories that a four-way box allows.