3.2 Choosing a Motherboard

You can sometimes upgrade a system cost-effectively without replacing the motherboard. The more recent the system, the more likely this is true. The easiest upgrade is always replacing a processor with a faster version of the same processor. Doing that may simply mean pulling the old processor and replacing it with the faster one, although a BIOS upgrade may also be needed. Alas, there is no guarantee that a given motherboard will support a faster version of the same processor or that a required BIOS upgrade will be available, and the rapid advances in processors means that a faster version of the same processor may no longer be available.

The next-easiest upgrade is to replace the processor with a later model from the same generation. For example, you may be able to replace a Pentium II/350 with a Pentium III/850 or, by using a slocket adapter, with a cheap, fast Celeron. When upgrading to a later-model processor, a BIOS upgrade will almost always be needed, and you should check the motherboard manufacturer's web site carefully to determine which configurations are supported.

Faster processors may draw more current, and the VRMs on an older motherboard may be inadequate to support the new processor. Even if the processor appears to work properly at first, running it for a while may damage both the motherboard and the processor. Always check to make sure that the exact processor you plan to install is supported by the motherboard.

It doesn't make sense to stretch an old motherboard too far. Just because you can upgrade a system without replacing the motherboard doesn't mean that you should do so. Motherboards are inexpensive, typically $75 to $150. Doing an in-place upgrade instead of replacing the motherboard leaves you with the limitations of the old motherboard and may limit the performance of the new processor. Before you decide to keep the motherboard, find out the costs and benefits of replacing it instead. Don't forget to factor in the supplementary benefits of a new motherboard—a better chipset and BIOS, support for the latest hard disk standards, etc. You may well decide it's worth spending the money to replace the motherboard. In fact, you may decide simply to retire the existing system to less demanding uses and build a new system.

Use the following guidelines when choosing a motherboard:

Decide which CPU to use

The CPU you choose determines the type of motherboard you need. Choose an Intel Celeron or Pentium III (Socket 370), an Intel Pentium 4 (Socket 478), or an AMD Athlon or Duron (Socket A) motherboard. Don't buy a motherboard that uses an obsolescent or obsolete CPU connector, such as Socket 7, Slot 1, Slot A, or Socket 423. With fast Socket 370, Socket 478, and Socket A processors available at very low prices, there is no point to buying into older technology, even though motherboards and processors using that technology may remain available.

Buy a motherboard that uses the right chipset

For a single Intel Pentium III or Celeron processor, we recommend the Intel 815E or 815EP chipset. For dual Pentium III processors, we don't much like any of the currently available alternatives, but the VIA Apollo Pro266T chipset is probably the least bad choice. For AMD Athlon or Duron processors, choose the SiS 735 or 745 for a single-processor system or the AMD-760MPX for a dual-processor system. For a mainstream Pentium 4 system, choose the Intel 845E or 845G chipset with DDR-SDRAM. For a performance Pentium 4 system, choose the Intel 850E chipset with PC800-40 or PC1066 RDRAM. For a P4-based Celeron system, choose the Intel 845GL chipset with DDR-SDRAM.

Make sure the motherboard supports the exact processor you plan to use

Just because a motherboard claims that it supports a particular processor doesn't mean that it supports all members of that processor family. For example, many motherboards support the Mendocino-core Celeron but do not support the Coppermine128-core Celeron. Similarly, many motherboards that support the Coppermine-core Pentium III do not support the Tualatin-core Pentium III. Make sure the motherboard supports the exact processor you plan to use before you buy it.

Choose a board with flexible host-bus speeds

Motherboards for Intel sixth-generation processors may support FSB settings of 66, 100, and/or 133 MHz. Ideally, choose a motherboard that supports all three settings for maximum flexibility. Otherwise, choose a motherboard that supports at least the settings you need now and expect to need for the life of the board—66 and 100 MHz for Celerons, and 100 and 133 MHz for Coppermine- and Tualatin-based Pentium IIIs. Older Athlon motherboards support only a 100 MHz FSB (which uses DDR for an effective 200 MHz), whereas newer AMD processors are available in both 100/200 MHz and 133/266 MHz versions, so even if you're installing a 100 MHz FSB processor, get a board that supports 133/266 for upgradability. If you must buy a Socket 7 board for some reason, make sure it supports the host bus speed of your processor. Boards that offer a full range of host-bus speeds—from 66 MHz to 100 MHz or higher, ideally in small increments—give you the most flexibility. If you intend to overclock your system, make sure the motherboard offers multiple choices of host-bus speed (again, the smaller the increments, the better) and allows you to set CPU voltage, ideally over a wide range in 0.05 volt increments.

Make sure the board supports the type and amount of memory you need

The choice here is among SDR-SDRAM, DDR-SDRAM, and Rambus RDRAM. Which is the best choice depends primarily on the processor you're using and on the best chipset to use with that processor. Both SDRAM memory types sell for about the same price, but DDR motherboards cost slightly more, all other things being equal. DDR has much higher bandwidth, but somewhat worse latency than SDR. RDRAM sells at a premium over either type of SDRAM, as do RDRAM motherboards, but RDRAM offers the best overall memory performance. Pentium III, Celeron, AMD Athlon, and Duron processors benefit only slightly from the additional bandwidth of DDR or RDRAM, because they are not usually memory-bound. Pentium 4 processors benefit significantly from DDR-SDRAM or RDRAM.

Our opinion is that for sixth-generation processors, using SDR versus DDR is a toss-up. We'd normally be slightly inclined to go with DDR-SDRAM, if only because DDR is the wave of the future, except that the best sixth-generation chipset for Intel processors is the Intel 815E, which does not support DDR-SDRAM. On that basis, we'd go with the 815E and SDR-SDRAM. For the Athlon and Duron, the situation is reversed. The best chipsets for those processors are the AMD-760MPX and the SiS 735, which are DDR chipsets, so we'd choose DDR-SDRAM. For the Pentium 4, there's no question. Go with the Intel 845E or 845G chipset and DDR-SDRAM for mainstream applications, or with the Intel 850E chipset and RDRAM for applications in which memory performance is an important issue.

For SDR-SDRAM, make sure the board supports PC133 memory, even if the CPU does not require it. For DDR-SDRAM, make sure the board supports PC2100 memory (and, ideally, the forthcoming PC2700 DDR-SDRAM), again even if the processor does not require it.

Do not make assumptions about how much memory a motherboard supports. A motherboard has a certain number of memory slots, and the literature may state that it accepts memory modules up to a specific size, but that doesn't necessarily mean you can install the largest supported module in all of the memory slots. For example, a motherboard may have four memory slots and accept 512 MB DIMMs, but you may find that you can use all four slots only if you install 256 MB DIMMs. Memory speed may also come into play. For example, the VIA Apollo Pro133A chipset supports four rows of PC100 SDRAM, but only three rows of PC133 SDRAM.

Also, chipsets and motherboards vary in terms of how much memory of different types they support. For example, the Intel 845 chipset supports up to 3 GB of SDR-SDRAM, but only up to 2 GB of DDR-SDRAM. Registered versus unbuffered memory may also be an issue. For example, although Tyan recommends (and we concur) that you use only Registered DDR-SDRAM with their S2460 Tiger MP dual-Athlon board, some have reported that the Tiger MP does work properly with unbuffered memory, but only if you limit it to one DIMM.

Nor do all motherboards necessarily support the full amount of memory that the chipset itself supports, even if there are sufficient memory sockets to do so. Always check to determine exactly what combinations of memory sizes, types, and speeds are supported by a particular motherboard.

For a general-purpose system, support for 256 MB of RAM is marginally acceptable, and 512 MB is better. For a system that will be used for memory-intensive tasks such as professional graphics, make sure the motherboard supports at least 512 MB of RAM, and 1 GB or more is better.

Although you may be able to find a new motherboard that supports migrating existing memory from the old motherboard, it's usually not a good idea to do so unless that older memory is current—i.e., PC133 SDRAM or later. Memory is cheap, and it seldom makes sense to base a new motherboard purchase decision on the ability to salvage a relatively small amount of old, slow memory.

Avoid hybrid motherboards

Every time there's a change in memory technology, some motherboard manufacturers make motherboards that accept both the older and newer types of memory. With the change from SDR-SDRAM to DDR-SDRAM, you can expect to see such hybrid motherboards. We think buying a hybrid motherboard is a mistake, both because we've yet to see one that worked well with both types of memory, and because hybrid motherboards are usually problematic in other respects as well. Motherboards are relatively inexpensive. If you want to use SDR-SDRAM, buy an SDR-SDRAM motherboard. If you want to use DDR-SDRAM, buy a DDR-SDRAM motherboard.

Check documentation, support, and updates

Before you choose a brand or model of motherboard, check the documentation and support that's available for it, as well as the BIOS and driver updates available. Some people think that a motherboard that has many patches and updates available must be a bad motherboard. Not so. Frequent patch and update releases indicate that the manufacturer takes support seriously. We recommend to friends and clients that they give great weight to—and perhaps even base their buying decisions on—the quality of the web site that supports the motherboard.

Buy a motherboard with the proper form factor

If you are building a new system, choose an ATX motherboard that best meets your needs, and then buy an ATX case and power supply to hold it. If you are upgrading an existing system that uses a BAT motherboard, choose a new BAT motherboard. But before you worry too much about reusing the BAT case and power supply, consider that good-quality ATX cases and power supplies are available for under $100. Most recent motherboards, including all AMD Athlon and Pentium 4 motherboards, are available only in ATX or one of its variants. You may be better off retiring the old case and buying a modern ATX case and motherboard.

The preceding issues are always important in choosing a motherboard, but there are many other motherboard characteristics to keep in mind. Each of them may be critical for some users and of little concern to others. These characteristics include:

Expansion slots

Any motherboard you buy will provide PCI (and possibly ISA) expansion slots, but motherboards differ in how many slots they provide. Three PCI slots is marginal, four adequate, and five or more preferable. Integrated motherboards—those with embedded video, sound, and/or LAN—can get by with fewer PCI slots. Using ISA slots should be avoided at all costs, so the number of ISA slots is largely immaterial. Having an AGP slot (2X or 4X) is a definite plus, even if the motherboard includes embedded video. Many recent motherboards include an Audio-Modem Riser (AMR) slot or Communications and Networking Riser (CNR) slot, which are designed solely to allow system manufacturers to embed low-end audio and communications functions cheaply. Anyone reading this book will disdain AMR and CNR, instead installing discrete sound and/or modem support. The presence or absence of an AMR or CNR slot is therefore immaterial, except that you would much prefer that the space occupied by that slot instead be used by another PCI slot.

Warranty

It may seem strange to put something generally regarded as so important in a secondary category, but the truth is that warranty should not be a major issue for most users. Motherboards generally work or they don't. If a motherboard is going to fail, it will likely do so right out of the box or within a few days of use. In practical terms, the vendor's return policy is likely to be more important than the manufacturer's warranty policy. Look for a vendor who replaces DOA motherboards quickly, preferably by cross-shipping the replacement.

Ports, connectors, and front-panel LEDs

Any new motherboard should provide at least two 16550A or better serial ports, one EPP/ECP parallel port, two USB ports, a keyboard port, and a mouse port. Many newer motherboards are so-called "legacy-reduced," which means that they lack serial, parallel, keyboard, and mouse ports. We avoid using those when possible, because there are simply too many times when "legacy" ports are useful. However, as time goes by it will be increasingly hard to avoid legacy-reduced motherboards because they'll eventually all be that way.

If you are upgrading an older system, you may need to either buy adapters separately for your keyboard and mouse or replace one or both of them. Also, depending on the motherboard and case, you may have to extend motherboard I/O ports to connectors mounted on expansion card brackets rather than on the back panel, which can make one or more expansion slots unusable. Make sure to ask which port connectors come with the motherboard. Many AT motherboards include a USB header, but the cable necessary to extend USB to the back panel may be a $10 option. Also check the documentation to determine how the header pins for front-panel switches and indicators are arranged on the new motherboard. It's quite common to find that existing cables aren't long enough to reach the connectors on the new motherboard, or that the new motherboard uses different pin arrangements for particular connectors.

Embedded sound and video

Some motherboards include embedded sound, video, and/or LAN adapters as standard or optional equipment. In the past, such motherboards were often designed for low-end systems, and used inexpensive and relatively incapable sound and video components. But nowadays many motherboards include "name brand" sound (e.g., SoundBlaster PCI), video (e.g., nVidia), and LAN (e.g., Intel or 3Com) adapters, making them good choices around which to build a mainstream mid-range system. Such motherboards are normally priced $25 to $50 higher than motherboards without the embedded peripherals, allowing you to save $50 to $150 by buying the integrated motherboard rather than separate components. If you buy such a motherboard, make sure that the embedded devices can be disabled if you later want to replace the embedded adapters with better components.

Embedded adapters often use the main CPU, which can reduce performance by a few percent. The speed of current processors means this is seldom an issue. However, if processor performance is critical, you may wish to use a motherboard that has few or no embedded functions.

Power management and system management

We regard power management as a useless feature and do not use it. It saves little power, increases the wear and tear on the equipment due to frequent power cycling, and tends to cause bizarre incompatibilities. We have experienced numerous problems with ACPI, with many different motherboards and operating systems, including systems that go into a coma rather than going to sleep, requiring a hard reboot to recover, and so recommend not using it at all. If for some reason you need power management, make sure the motherboard you buy supports at least a subset of the ACPI specification. Most current motherboards support some ACPI functions, but determining exactly which requires detailed examination of the technical documents for that motherboard.

System management is usually unimportant outside a corporate environment. If system management is an issue for you, look for a motherboard that supports all or some of the following features: voltage monitoring, CPU and/or system temperature sensors, chassis intrusion alarm, and fan activity monitoring for one or more fans.

Wakeup functions

Again, these features are primarily of interest to corporate IS folks rather than individual users. But if wakeup functions are important to you, you can buy a motherboard that supports "wake-on" some or all of the following: LAN activity, modem ring-in, keyboard/mouse activity, and real-time clock.

Jumperless (or single-jumper) configuration

Older-style motherboards are configured mostly by setting jumpers. Recent motherboards use fewer (or no) jumpers, depending instead on CMOS Setup to configure motherboard settings. A board that uses CMOS Setup is marginally easier to configure than one that uses jumpers.

Boot devices supported

Any motherboard supports booting from the hard drive or the floppy drive. Most modern motherboards also support booting from El Torito-compliant CD-ROM drives and from floppy-replacement drives like the LS-120 and/or Zip drive. If boot support is an issue for you, make sure the motherboard you buy supports booting from your preferred device. Also make sure that CMOS Setup allows you to specify a boot sequence that allows you to make your preferred device the primary boot device.

Minor or special-purpose features

Motherboards attempt to differentiate themselves by including various minor features, such as IRDA port or additional fan power headers (at least one is needed for the CPU fan, but some motherboards include two or three power headers to support supplemental fans).