Build Your Own Dual-Processor Server

Before you read on, heed this warning: Do not try to assemble your own mission-critical server. You are better off purchasing a system from a mainstream hardware vendor to run mission-critical applications. Vendors can address your support, repair, and parts needs for systems you purchase from them, but you're responsible for providing support, repair, and parts for a server you build. Most organizations don't want to risk running essential applications on home-built systems.

Despite this warning, you have plenty of opportunities to roll up your sleeves and build a server. Non-production test systems; servers that aren't mission-critical, such as print servers; and even some infrastructure servers, such as Dynamic Host Configuration Protocol (DHCP) or routing servers, can be candidates for low-cost, build-it-yourself platforms.

Building your own dual-processor Windows NT server costs about the same as buying a high-end single-processor machine, plus a couple hundred dollars for the second CPU. You need the same Error-Correcting Code (ECC) RAM, SCSI disk subsystem, video subsystem, and incidentals (including the case, keyboard, and mouse) for single- and dual-processor systems. If you're upgrading a system rather than building the server from scratch, you can salvage many of these components from the existing machine. The only components you definitely must buy are a new motherboard and at least one CPU.

Mother of All Choices
Multiprocessor motherboards are similar to single-processor motherboards, but multiprocessor motherboards include additional circuitry to support symmetric multiprocessing (SMP) and an additional socket for a second CPU. Different SMP motherboards offer a variety of extras, such as onboard SCSI adapters, video adapters, and sound cards.

Before you select extra features for your motherboard, you must decide whether you want to use Pentium, Pentium Pro, or Pentium II processors. You must choose Pentium-class CPUs­ Advanced Micro Devices (AMD) and Cyrix CPUs won'twork on a multiprocessor NT system.

Pentium-class processors can use Advanced Programming Interrupt Controller (APIC), Intel's chipset standard for SMP technology. AMD and Cyrix processors use a different standard, OpenPIC, which NT doesn't currently support. Table 1, page 82, lists several multiprocessor Pentium, Pentium Pro, and Pentium II motherboards you can choose from and includes each motherboard's feature set.

If you want to upgrade a single-Pentium machine, your cheapest option is to upgrade to a dual-Pentium system. Many mail-order establishments sell 200MHz Pentium CPUs for less than $200 and dual-Pentium motherboards cost only marginally more than single-Pentium motherboards. Without memory, onboard SCSI cards or NICs, or other extra components, dual-Pentium mother-boards range in price from $175 to $300.

If you want to maximize your CPU power, you'll be interested in the Pentium II processor. This solution is expensive. The fastest Pentium II CPUs (333MHz) cost more than $700 each from mail-order firms, and at least $800 from local suppliers. In addition, the Pentium II platform currently lacks scalability; only two CPUs fit on multiprocessor Pentium II motherboards. Don't build a dual-Pentium II system if you might need to add more CPUs to your server within the foreseeable future.

If you want a reasonable compromise between slow, inexpensive Pentium processors and fast, high-cost Pentium II processors, you can build a multi-Pentium Pro server. The fastest Pentium Pro processor is 200MHz, with a 512KB Level 2 cache. Independent lab tests have demonstrated that 200MHz Pentium Pro processors perform application- and file-server functions only marginally slower than 300MHz Pentium II CPUs, presumably because of the Pentium Pro processor's faster Level 2 cache. You can purchase a 200MHz Pentium Pro processor with a 256KB Level 2 cache for about $500. The same CPU with a 512KB Level 2 cache costs roughly $200 more.

The disadvantage of implementing a Pentium Pro SMP solution is that Intel has announced it will discontinue Pentium Pro processor production, and many motherboard vendors are phasing out production of Pentium Pro motherboards. You'll probably have trouble upgrading a dual-Pentium Pro system to include more processors in the future. In addition, you might not be able to replace existing parts, so a motherboard failure could leave you stuck with two or more orphaned CPUs.

After you decide which CPU platform you want to use, you need to evaluate the features available on motherboards designed for that platform. Some motherboards include a built-in VGA port for connecting a monitor. Many motherboards include an onboard Adaptec SCSI controller for connecting SCSI devices internally. In addition, some high-end Pentium and Pentium Pro motherboards provide multiprocessing power through a backplane and daughterboard. The daughterboard contains the CPU circuitry, so the next time you want to upgrade your system, you just replace the daughterboard. The backplane is similar to a typical motherboard, except that it has a special expansion slot where the daughterboard plugs in. The only problem with this configuration is that the backplane's expansion slot for the daughterboard might cramp your PCI, EISA, or Accelerated Graphics Port (AGP) expansion slots or reduce the number of expansion slots the backplane can hold.

Evaluate the motherboards available for the platform you're considering, and determine which features are important to you. Each feature adds value, but it also increases the motherboard's price, and it might require you to purchase additional hardware. If you don't need a feature, you're better off buying a motherboard without it.

Extra Hardware
To upgrade a system from one CPU to two CPUs, you might need to install replacement RAM. If you are running a single-processor NT server, you probably have 72-pin Enhanced Data Output (EDO) SIMMs, or perhaps 72-pin fast-page-mode SIMMs with parity. If the new server's reliability is paramount, you'll require ECC SIMMs. RAM prices fluctuate daily, but you can estimate your RAM costs based on the current price for a 64MB ECC SIMM, $140.