CIS 107a: Introduction to Hardware Concepts

Chapter 5: The Motherboard



This chapter discusses features of motherboards. The objectives important to this chapter are:

  1. Recognizing and selecting types of motherboards
  2. Configuring a motherboard
  3. Installing a motherboard
  4. Troubleshooting a motherboard

The chapter begins with a repetition of material from the chapter on form factors. A form factor is defined as a size, shape, and set of features. The author observes that, when building a computer, you should pick a form factor for the motherboard first, which will limit or determine your choices for the case and the power supply. Review the basic requirements:

  • the motherboard must be small enough to fit in the case, and the holes in it must match the attachment points in the case
  • the ports (jacks) on the motherboard must match holes in the case
  • the power supply must fit in the case, and must have power cords that fit the motherboard and provide the correct amount of power

This chapter lists even more types of system boards than the form factor chapter. This list divides them into groups:

  • ATX (ATX, Enhanced ATX, MiniATX, MicroATX, and FlexATA)
  • BTX (BTX, MicroBTX, NanoBTX, and PicoBTX)
  • NLX
  • AT (AT and Baby AT). Each has variations.

In addition to form factor questions, the text offers several more considerations when choosing a motherboard, as a replacement item or as the original part for a new computer:

  • Which processors will fit the socket/slot on the motherboard?
  • What bus speeds are provided?
  • What chipset is on the motherboard?
  • What kind of memory can be used, how much of it, and what are the possible configurations? (Very important questions if you mean to re-use memory you already have.)
  • What expansion slots are on the motherboard, and how many of each?
  • What sockets and jacks are included?
  • What devices are built into the motherboard? (e.g. Wi-Fi, video, sound)

A discussion of buses and slots begins on page 182. Page 183 shows several illustrations of connectors on cards made for several kinds of slots. Follow this link to an Internet page with similar illustrations. You should have an understanding of each kind of bus described:

  • System bus - the main bus on the motherboard that connects directly to the processor
  • AGP bus - slots are usually brown, the smallest kind of slot so far, two connector sections (short one toward the access cutouts), and recessed farther away from the access cutouts than any other slot.
  • PCI bus - PCI slots are usually white, smaller slots with two connector sections (the longer one toward the access cutouts if they are standard PCI slots). PCI devices share a common interrupt request line through IRQ steering
  • PCI Express - an improved version of the PCI bus, PCI Express has connections to both the North Bridge and the South Bridge of the chipset
  • VESA Local bus - VESA buses were created to meet the need for faster video. VESA has three connector sections, and older than the two slot designs above.
  • FireWire - also called IEEE 1394, this is meant to be a connection for faster devices. Up to 63 devices can be daisy-chained. Windows 98, NT and later versions support FireWire, as does the Macintosh operating system.
  • MCA bus - the Microchannel architecture bus from IBM was the first 32 bit bus, and was a proprietary design, making it a marketing failure.
  • EISA (Extended ISA) bus - invented as a response to IBM's MCA bus. The slots resemble 16 bit ISA slots, but EISA slots are deeper, to accommodate the double row of contacts on the EISA card's connector. The 16 bit contacts are the upper row, the 32 bit contacts are the lower row. An ISA card will fit in one of these slots and work, because it will only go about halfway into the EISA slot, engaging only the 16 bit contacts.
  • ISA bus - Industry Standard Architecture, comes in 8 bit and 16 bit versions. Older 8 bit ISA cards are expected to work in 16 bit ISA slots, unless the card has a skirt that prevents inserting it in a 16 bit slot. (The skirt was meant to act like a bicycle stand for the card.)
  • USB - universal serial bus is meant for "slow" devices. Version 1 can support connections that flow at speeds up to 1.5 Mbps (Megabits per second) or 12 Mbps. Version 2 supports faster data rates. Devices can be daisy-chained (up to 127 devices). Windows 98 supports USB, if drivers are used. Windows 2000 and later support it natively.

Ports can be directly connected to the system board, or they may appear on expansion cards. If you have a system with onboard ports, you may want to determine how to override them, or shut them off, in case they go bad. As noted above, an onboard port can be convenient if it suits your needs and inconvenient if you want to upgrade or replace it.

Motherboards require some configuration when installed, or when some components are added or replaced. Older technologies, like setting IP switches and placing jumper covers over specific pins may still be used. It is also common to configure some settings in CMOS.

It may be valuable for technicians to know some of the common keypress combinations required to enter the CMOS setup program for various BIOS manufacturers. Several are listed in the text. However, the best procedure for getting into the setup menu is to turn on a monitor a minute before you start the computer, then watch carefully for the instructions that will appear on the screen a moment before the operating system loads. You will need to read the instruction and follow it before the OS starts, or you will have to shut down the computer and try again at another cold boot.

Facts to remember about CMOS settings:

  • CMOS chips retain their settings by a trickle charge from a rechargeable battery on the motherboard. This battery is recharged while the computer runs, so it can lose its charge if the computer is not turned on for a long time.
  • CMOS settings usually include an optional password. If a password is set, a user cannot start the computer without knowing it. However, there is usually a jumper setting that can be changed on the motherboard to erase this password, so it provides security from users, but not from technicians.
  • The CMOS setup program is typically held on one BIOS chip, which can usually be updated with a download from the manufacturer.

Students should review the author's instructions for removing and installing a motherboard. When replacing a motherboard with a new one from a different manufacturer, it is very important to place components in the right place in the new board. Reading the manufacturer's instructions will help a great deal. So will studying the old motherboard carefully before removing the components from it.