[Technology Report]
High-Performance PC Platforms Push Tomorrow's Technology
Multiprocessor system design gets more complex as new technologies like InfiniBand and HyperTransport come online.
System designers have a number of choices when it comes to multiprocessor system architectures. Many of the components are common to single-processor designs. Some new technologies, such as Serial ATA and InfiniBand, will wind up in both single-processor and multiprocessor systems (see the figure).
Of course, the performance obtained from any multiprocessor system is only as good as the individual components it comprises, mainly the processor and memory types. So, choosing the right combination of processor, memory, supporting chip sets, and peripheral functions, as well as local and peripheral buses, is necessary to best match the application in mind. Designers have a wide selection of processors, and supporting chip sets are available to work with, while even higher-performance versions are waiting in the wings.
Symmetrical multiprocessor systems (SMPs) typically employ identical processors, with 32-bit systems giving way to 64-bit processors at the high end. Sun's UltraSparc, Compaq's Alpha, and IBM's PowerPC are 64-bit processors incorporated into the respective companies' SMP offerings. They have shown up in offerings from other vendors too, with IBM's PowerPC as the most popular.
Intel's much-anticipated IA-64 very-long-instruction-word (VLIW) processor architecture has also garnered the interest and support of vendors. The first of the IA-64 processors, the Itantium, is finding a home in evaluation and development systems. SMP systems are included in this collection, but broad commercial distribution will probably occur with the chip code-named McKinley. The IA-64 looks like the one to watch over the long term, although Sun's UltraSparc has a rather large head start.
The x86-64 from Advanced Micro Devices (AMD) is the virtual dark horse. It has been announced, but samples aren't available yet. The major advantage to x86-64 is the way that it extends the x86 architecture instead of replacing it as Intel does with the Itantium.
The Itantium runs 32-bit x86 code, but the native 64-bit code is completely different. Plus, the VLIW approach requires investment in new development and debugging tools. AMD's approach requires new development and debugging tools too, but they only need relatively small, incremental changes from the x86 tools that are already well established.
The x86-based 32-bit processors dominate the midrange. Currently, Intel's Pentium III and Xenon are the workhorses in two- to eight-processor systems. The new Pentium IV is now used in the single-processor space but is expected to replace the Pentium III and Xenon processors in most new designs. It will have to compete with the IA-64 processors. The big question is where the boundary will wind up. While x86 applications have the stability from years of development and deployment, the IA-64 has yet to prove itself.
AMD's Athlon has pushed its way into the 32-bit single-processor realm with great success. Although they're late to the SMP arena, dual-processor Athlon systems are due soon. But whether the Athlon will make a dent in systems with more than two processors remains to be seen.
Dual-processor system designs are popular because the bandwidth of the processors, memory, and chip sets allow two processors to run at full speed without radically changing system designs, compared to a single-processor system. In fact, most dual-processor motherboards are identical to their single-processor counterparts, except for a second processor socket and a change in chip-set numbers.
Intel, VIA Technologies, and Broadcom ServerWorks Group sell dual-processor chip sets, on which the majority of dual-processor motherboards are based. ServerWorks ServerSet chip set is the only product line that expands past two processors.
These chip sets target the x86 space with support for the Intel Pentium III and Xenon processors. Intel's 840 chip set is one of the most commonly used dual-processor chip sets. Its 82840 Memory Controller Hub supports 2x/4x AGP video ports and has dual RDRAM channels. The companion 82801 I/O Controller Hub ties two processors to PCI, IDE and USB peripherals.
AMD's AMD-761 chip set will allow Athlon to move into the SMP space. It had been restricted to single-processor systems where it became very popular. Meanwhile, the AMD-761 supports DDR-SDRAMs running at 100/200 MHz or 133/266 MHz, a 33-MHz 32-bit PCI bus, and 4x AGP video. Its specifications are a little less impressive than those available for the Intel processors, but the AMD-761 provides more than enough power for the majority of dual-processor workstations and servers. Additional third-party, dual-processor chip-set support for the Athlon is expected in the future.
Dual processors are standard fare in the server market, with quad- and eight-processor systems becoming more common as thin-client support, database servers, and Web-based application servers grow in importance. These configurations are found in embedded applications like telephone switching systems too, where performance and reliability are key. Such configurations need a significantly different design approach from dual-processor systems.
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