What Is a Motherboard

Choosing a Motherboard ¶ 

Two fundamental characteristics determine whether a motherboard is suitable for upgrading a particular system:

Form factor ¶ 

The form factor of a motherboard defines its physical size, mounting hole locations, and other factors that determine whether the motherboard fits a particular case. The vast majority of computers made since 1995 use either the ATX form factor, also called full ATX, or the microATX form factor, also called ATX. A microATX motherboard fits a microATX case or an ATX case; an ATX motherboard fits only an ATX case. [ch04.html#repairpc-CHP-4-FIG-2 Figure 4-2] shows a typical microATX motherboard on the left, with a larger ATX motherboard on the right.

If your current case accepts ATX or microATX motherboards and has a compatible power supply, upgrading the motherboard is a simple matter of removing the old motherboard and replacing it with the new one. Alas, some systems primarily cheap, mass-market units use nonstandard proprietary motherboards and/or power supplies. If the motherboard in such a system fails, that system is good for little more than the scrap heap. You may be able to salvage the processor, memory, drives, and other peripherals, but the case and motherboard are useless.

Figure 4-2. Typical microATX (left) and ATX motherboards

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FIXME rbug_0402.png Typical microATX (left) and ATX motherboards

IF A IS GOOD, B MUST BE BETTER

In 2004, Intel began shipping motherboards based on a new form factor, called BTX (Balanced Technology eXtended). Although BTX is a derivative of ATX, BTX cases and motherboards are physically incompatible with ATX components. Intel had hoped that BTX would take the market by storm, but as of early 2006 BTX had made only minimal inroads in the PC market.

BTX may be a solution in search of a problem. The original goal of BTX was to improve cooling at a reduced noise level: a necessary improvement, given the very high heat production of Intel Pentium 4 processors, some of which consume 130W. Now that Intel is shifting processor production to low-power cores that consume as little as 20W, there is no longer a real need for BTX.

More Trouble than They're Worth

For all practical purposes, a processor that is designed to fit one socket cannot be installed in another type of socket. Socket adapters are available to shoehorn one type of processor into another type of socket e.g., a Socket 479 Pentium M processor into a Socket 478 motherboard but such adapters often have compatibility issues. We recommend you avoid socket adapters.

Processor socket type ¶ 

Modern processors connect to the motherboard via a processor socket. The processor has an array of hundreds of pins that fit into matching holes on the processor socket. [ch04.html#repairpc-CHP-4-FIG-3 Figure 4-3] shows an mPGA478 socket, which accepts an Intel Pentium 4 or Celeron processor, a typical processor socket. Sockets designed to accept other types of processors are similar in appearance, but with a different number and arrangement of holes.

Figure 4-3. A typical processor socket

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FIXME rbug_0403.png A typical processor socket

Most current processor sockets use a ZIF lever (Zero Insertion Force lever) to secure the processor in the socket. This lever, visible on the right edge of the socket, is raised to install the processor. Raising the lever removes the clamping force inside the socket, and allows the processor to be dropped into place without applying pressure. After the processor is seated in the socket, lowering the ZIF lever clamps the processor into place and ensures good electrical contact between the processor pins and the socket contacts.

Identify Your Socket

You can identify the socket type used by your current motherboard by checking the documentation, by looking up the motherboard model number on the Internet, or by running a diagnostic utility such as Everest (http://www.lavalys.com) or SiSoft Sandra (http://www.sisoftware.net). You can also identify the socket type unambiguously by examining the socket itself, although that will require removing the processor cooler and perhaps the processor itself.

MALE SOCKET, FEMALE PROCESSOR

Intel Socket 775 is the exception among modern processor sockets. Socket 775 reverses the usual arrangement of male processor and female socket by putting the pins in the socket and the holes in the processor. Socket 775 also dispenses with the ZIF lever, using a different clamping arrangement to secure the processor in the socket.

[ch04.html#repairpc-CHP-4-TABLE-1 Table 4-1] lists the processor sockets that have been used on recent systems. Systems based on processor sockets listed as obsolete Slot A, Slot 1, and Socket 423 are not practically upgradable, because motherboards and/or processors are no longer readily available with those sockets. By that, we mean that it isn't practical to upgrade the motherboard and processor unless you replace both; it's still feasible to install more memory, replace the drives, and make other upgrades to such systems.

Table 4-1. Processor socket types

FIXME TABLEWASHERE

Systems that use one of the sockets we list as obsolescent Sockets A, 478, and 754 are reasonably good upgrade candidates. Although processors and motherboards are no longer under active development for obsolescent processor sockets, motherboards that use those sockets are readily available and likely to remain so for some time, as are processors to fit those New Lamps for Old sockets.

New Lamps for Old

Installing an older processor in a newer motherboard seldom presents any problems, although you should always verify that your old processor is explicitly listed as supported by the new motherboard (taking into account the motherboard revision level). Installing a newer processor in an older motherboard may be problematic, because the newer, faster processor may draw more current than the motherboard is designed to supply.

WHEN SOCKET TYPE DOESN'T MATTER

Of course, if you plan to replace not just the motherboard, but the processor and perhaps memory as well, the type of socket used by the current motherboard and processor is immaterial. You can simply choose the best processor and compatible motherboard to fit your needs and budget.

Choosing a motherboard ¶ 

Because the motherboard controls the system, it pays to select one carefully. The motherboard you choose determines which processors are supported, how much and what type of memory the system can use, what type of video adapters can be installed, the speed of the communication ports, and many other key system characteristics. In addition to choosing the correct form factor and processor socket, which are essential, use the following guidelines when choosing a motherboard:

Choose the right chipset. ¶ 

The chipset acts like an administrative assistant to the processor. It handles what goes in and what comes out and takes care of all the ancillary functions that make it possible for the processor to compute.

The chipset determines which processors and types of memory are supported, as well as which of the two video adapter standards, AGP or PCI Express, the motherboard supports. The chipset also determines which embedded features such as USB 2.0, Serial ATA, FireWire, video, audio, and networking are available. Chipsets vary widely in performance, features, compatibility, and stability. [ch04.html#repairpc-CHP-4-TABLE-2 Table 4-2] lists the chipsets we recommend by socket type.

Table 4-2. Recommended chipsets by socket type

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  • If you are replacing a failed motherboard and plan to use your current processor, choose a motherboard that has the correct socket type and uses one of the recommended chipsets. If your current memory and/or video adapter are worth salvaging, also take into account their compatibility with the replacement motherboards you are considering.
    • If you are buying a new AMD processor, choose a Socket 939 nForce3 motherboard (for AGP video) or nForce4 motherboard (for PCI Express video).
    • If you are buying a new Intel processor, choose a Socket 775 motherboard that uses an Intel 945- or 955-series chipset that supports the type of video card you plan to install.

Chipsets for AMD and Intel processors are made by several other companies, such as VIA and SiS, but we have found that the performance and compatibility of these alternative chipsets leaves something to be desired. Motherboards based on Intel and NVIDIA chipsets are a bit more expensive than those based on alternative chipsets, but the small additional cost is well worth it.

Bad Cooks Ruin Good Ingredients

Although it is impossible to build a good motherboard with a poor chipset, it is quite possible to build a poor motherboard with a good chipset. We use and recommend Intel or ASUS motherboards for Intel processors and ASUS motherboards for AMD processors.

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

Just because a motherboard claims to support a particular processor doesn't mean it supports all members of that processor family. For example, some motherboards support the Pentium 4 processor, but only slower models. Other motherboards support fast Pentium 4s, but not slower Pentium 4s or Celerons. Similarly, some motherboards support the Athlon with a 200, 266, or 333 MHz FSB, but not the 400 MHz FSB.

Advice from Ron Morse

There's an even better reason to demand the latest motherboard revision level: subtle engineering changes to the components used, board layout, or other engineering factors may be "slipstreamed" into production based upon reported problems from early production runs. These are usually subtle things. You notice them when you repeatedly beat up customer support over a recurring problem, they suddenly agree to RMA the unit, and you find the new one works flawlessly in what is otherwise the same system. I'm convinced this happens a lot. ATI RADEON 9700 Pro video cards are a prime example, and Tyan 1840 series motherboards another.

CLOSE ENOUGH ISN'T

Make sure the motherboard supports the exact processor you plan to use, before you buy it. To do so, visit the motherboard manufacturer's web site and look for the "supported processors" page for the exact motherboard you plan to use. Note that motherboard makers often "slipstream" revised models with the same model number, and the list of supported processors almost always assumes you are using the current motherboard revision. Quite often, an earlier revision does not support all of the processor models or speeds supported by a later revision. When you buy a motherboard, make sure to get the latest available revision.

Choose a board with flexible host bus speeds. ¶ 

Choose a motherboard that supports at least the settings you need now and that you expect to need for the life of the board. For example, even if you are installing an existing 400 MHz FSB Socket 478 Celeron initially, choose a motherboard that also supports Pentium 4 processors using the 533 and 800 MHz FSB speeds. Similarly, even if you are installing an old 266 MHz FSB Athlon at first, choose a motherboard that supports the full range of Athlon FSB speeds 200, 266, 333, and 400 MHz. Boards that offer a full range of host bus speeds, ideally in small increments, give you the most flexibility if you later decide to upgrade the processor.

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

Any motherboard you buy should support current memory modules; that is, PC3200 DDR-SDRAM or DDR2 DIMMs. 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 mean you can necessarily 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, a particular motherboard may support three or four PC2700 modules, but only two PC3200 modules.

For a general-purpose system, support for 1 GB of RAM is acceptable. For a system that will be used for memory-intensive tasks, such as professional graphics, database management, or complex scientific calculations, make sure the motherboard supports at least 2 GB of RAM.

Unused Versus Unusable

Don't assume that you can use all available memory slots. For example, many early Socket 754 Athlon 64 motherboards provided three or even four DIMM slots, but could actually support only two memory modules reliably, regardless of the size or speed of those modules. 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 determine exactly what combinations of memory sizes, types, and speeds are supported by a particular motherboard.

DON'T BE PENNY WISE AND POUND FOOLISH

Although you may be able to find a new motherboard that allows you to migrate existing memory from your old motherboard, it's usually not a good idea to do so unless that older memory is current i.e., PC3200 DDR-SDRAM or DDR2-SDRAM. Memory is cheap, and it makes little sense to base a new motherboard purchase decision on the ability to salvage a relatively small amount of old, slow, cheap memory.

Make sure the motherboard supports the type of video you need. ¶ 

Motherboards differ in the provisions they make for video. Some motherboards provide an embedded video adapter and make no provision for installing a separate video adapter card. Other motherboards provide embedded video, but also provide a special expansion slot that accepts a standalone AGP or PCI Express video adapter card. Still other motherboards do not provide embedded video, but only an AGP or PCI Express slot that accepts a separate video adapter card. We recommend avoiding the first type of motherboard, even if you think embedded video is sufficient for your needs.

Check documentation, support, and updates. ¶ 

Before you choose a 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 true. 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. For examples of good motherboard support sites, visit Intel (http://www.intel.com/design/motherbd/) or ASUS (http://support.asus.com).

Choose the right manufacturer. ¶ 

Manufacturers differ greatly in the quality of the motherboards they produce. Some manufacturers, such as Intel and ASUS, produce only first-rate motherboards. (For that reason, we strongly prefer to use Intel or ASUS motherboards for Intel processors, and ASUS motherboards for AMD processors.) Other manufacturers produce motherboards of varying quality; some good and some not so good. Still other manufacturers produce only junk.

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

Number and type of expansion slots ¶ 

Any motherboard provides expansion slots, but motherboards differ in how many slots they provide, and of what types:

PCI slots ¶ 

PCI (Peripheral Component Interconnect) slots have been the standard type of expansion slot for more than a decade. PCI slots accept expansion cards such as LAN adapters, sound cards, and so on that add various features to a system. PCI slots are available in 32-bit and 64-bit versions, although 64-bit PCI slots are commonly found only on server motherboards.

Video slot ¶ 

A motherboard may have zero, one, or two dedicated video card slots. If a video slot is present, it may be AGP or PCI Express (PCIe), which are incompatible but serve the same purpose. The type of video slot determines the type of video card you can install. AGP video adapters are still popular and widely available, but PCI Express is fast becoming the dominant video adapter slot standard. Buy an AGP motherboard only if you have an AGP adapter that is worth saving. Otherwise, buy a motherboard, with or without embedded video, that provides a PCI Express x16 video slot. Do not buy any motherboard that provides embedded video but no separate video slot.

PCI Express slots ¶ 

Many motherboards with a PCI Express x16 video slot also provide one or more PCI Express x1 general-purpose expansion slots, usually in place of one or two of the PCI expansion slots, but sometimes in addition to them. For the immediate future, PCI Express x1 slots are relatively useless, because there are few expansion cards that fit them. However, as PCI Express x16 video cards increasingly dominate AGP, it's likely that PCI will also gradually fade away and that PCI Express x1 expansion cards will become more common.

ATX AGP motherboards typically provide five or six PCI slots. ATX PCIe motherboards typically substitute one or two PCIe x1 slots for one or two of the PCI slots. A microATX motherboard of either type typically provides two or three fewer slots than a full ATX motherboard. Years ago, many PCs had all or nearly all of their slots occupied. Nowadays, with so many functions integrated on motherboards, it's common to see PCs with at most one or two slots occupied, so the number of slots available is much less important than it used to be. It's still important to get the types of slots you want, though.

OEM versus retail-boxed packaging ¶ 

The same motherboard is often available as an OEM product and a retail-boxed product. (In fact, both forms of packaging are sold in retail channels.) The motherboard is identical or closely similar in either case, but there are differences. For example, the OEM version might have only a one-year warranty, while the retail-boxed version of the same motherboard has a three-year warranty. Also, the retail-boxed version often includes cables, adapters, a case label, a setup CD, and similar small parts that are not included with the OEM product. We generally recommend buying the retail-boxed version if it costs no more than $10 extra. Otherwise, buy the OEM version. You can download the setup CD and other software that isn't included with the OEM version.

VARIATIONS ON A THEME

There may be variations in the actual product between OEM and retail-boxed motherboards. For example, Intel often manufactures three to six variants of a motherboard, which may differ in minor ways (such as board color) and in more significant ways, such as the speed of the embedded network adapter, whether FireWire support is included, and so on. Some of these variants are available in both OEM and retail-boxed forms, and others in only one form or the other. Some variants aren't available to individual buyers. They're sold only in what Intel calls "bulk packaging," which means that the minimum order is a pallet load. Only large system makers buy bulk Intel motherboards.

Warranty ¶ 

It may seem strange to minimize the importance of warranty, but the truth is that warranty should not usually be a major consideration. 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 and connectors ¶ 

At a minimum, the motherboard should provide four or more USB 2.0 ports six or eight is better and a dual ATA/100 or faster hard disk interface. Ideally the motherboard should also provide at least two Serial ATA connectors, and four is better. (Some motherboards with four SATA connectors include only one parallel ATA interface, which is acceptable.) We also like to have a serial port, an EPP/ECP parallel port, a PS/2 keyboard port, a PS/2 mouse port, and an FDD interface, but those "legacy" ports are fast disappearing, replaced by USB.

Embedded sound, video, and LAN ¶ 

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 audio and video components. But nowadays many motherboards include very capable audio, video, and LAN adapters, and cost little or no more than similar motherboards without the embedded peripherals. 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.

Be Wary of Integrated Gigabit Ethernet

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 might wish to use a motherboard that has few or no embedded functions.

Embedded Gigabit Ethernet is a particular concern. If you buy a motherboard with embedded Gigabit Ethernet, make sure it uses a dedicated communications channel, such as the Communications Streaming Architecture (CSA) channel used by Intel chipsets or a PCIe channel. Some inexpensive motherboards have embedded Gigabit Ethernet adapters that connect via the PCI bus. That's a problem because Gigabit Ethernet is fast enough to saturate the PCI bus and noticeably degrade system performance.

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