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Intel Pentium II Processor
Intel CPUs are the most popular choice for commodity computing due to Intel's complete domination of the commodity computer market. Intel's Pentium II processor family currently ranges up to 450MHz CPUs with 100MHz memory bus speeds. However, its 512KB of L2 cache runs at half the speed of the processor. The Pentium II processors are limited to two CPUs in SMP systems.

Intel's inexpensive Celeron CPU with 128KB L2 cache may perform adequately, depending on the application. The Celeron's memory bus runs at 66MHz and its cache is one fourth the size of the Pentium II's. The Celeron's cache runs at the same speed as the processor, which helps overcome the penalty of the memory bus speed and small cache size. The stock Celeron may not be used in SMP systems, although with a hardware modification (which is reasonably easy to do using Socket 370 Celerons with "Socket 370 to Slot 1" converter boards such as the MSI MS-6905) it can be used in dual-CPU SMP systems.

Intel's Pentium II Xeon processors have a full speed cache of 512KB or 1024KB and a 100MHz memory bus. Xeons are expensive and require a different motherboard than the Pentium II or Celeron CPUs. Intel's 450NX chipset for the Xeon finally supports 64-bit PCI busses, which could improve communication performance on Gigabit-performance interconnects. The 450NX chipset also supports 4-way interleaving, which may help overall performance in an SMP system. Up to four Xeons can be used in an SMP system.

Intel-compatible CPUs are offered by vendors such as AMD and Cyrix, but they do not have comparable floating point performance.

Tom's CPU Guide provides a convenient comparison of Intel and compatible CPUs. Unfortunately, the CPU comparison doesn't appear to have been updated to include the newer Pentium II offerings.

The Compaq/Digital Alpha CPU is a strong competitor with the Intel CPUs. Our work with a cluster of 533MHz Alpha systems shows much higher floating point performance than can be obtained from Intel CPUs.


Pentium Pro Motherboard
Commodity motherboards tend to vary by chipset, cache, supported memory technologies, and processor support. The majority of the motherboards in production today use an Intel chipset for the PCI bus, but each manufacturer's board may perform differently even when identical memory and CPUs are used. We will focus on Intel-based systems, but commodity Digital Alpha systems have similar choices.

The choice of CPUs seems to be the major issue, as it is one of the most important components on the motherboard. The choice of L2 cache (if any), chipset, and RAM may all depend on the CPU choice.

Cache Choices

The choice of cache may be determined by the CPU selection: the Pentium II, Celeron and Xeon processors have built-in L2 cache. The Pentium II has a 512KB L2 cache, the Celeron has 128KB of L2 cache, and the Xeon has either 512KB or 1024KB of L2 cache. Up to two Pentium II CPUs can be combined in a dual-CPU symmetric multi-processor (SMP) configuration while four Xeon CPUs can be grouped in an SMP system.

Some Digital Alpha systems offer a large third level (L3) of cache to help improve performance.

Chipset Considerations

The chipset used by the motherboard may limit both the amount and type of RAM that can be used; for example, the Intel 440LX is the first Intel chipset to support SDRAM, a new RAM technology that provides faster memory bandwidth than FPM, EDO, or BEDO technologies.

The choice of chipset may also decide whether non-parity, parity, or ECC memory can be used. In a large group of systems, we feel that it is important to use ECC memory because of the large number of individual components (memory chips) that could fail.

Beware of any chipset or processor limitations that cause the system to cache only a portion of the full amount of RAM on a system. Performance will be tremendously reduced when accessing regions of memory that are not cacheable. The older Pentium II's (233MHz-333MHz) integrated L2 cache will only cache up to 512MB of memory. The newer Pentium II (350MHz and up) and Pentium II Xeon CPUs are capable of caching 1GB to 8GB of RAM, depending on the Pentium II model and chipset used.

The processor and chipset define the memory speed and PCI bus speed. On Celeron and slower Pentium II's, the memory bus speed is 66MHz and the PCI bus speed is 33MHz. Newer Pentium II's and Xeons run the memory bus at 100MHz. A faster memory bus affects the RAM speed selection (and in turn, price) and improves memory bandwidth.

Tom's Chipset Guide gives a nice table describing each chipset's technical features.

The bottom half of Tom's Mainboard Guide offers a set of motherboard performance comparisons and reviews.

Motherboard Vendors

There are many potential vendors; here's a quick, short list: At Ames Lab we have worked with SuperMicro, Tyan, and ASUS motherboards with Pentium Pro and Pentium II CPUs.

Appearance of any vendor in this list does not constitute endorsement of that vendor by Ames Laboratory.

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