CHAPTER 4 Motherboards and Buses 05 0789729741 Ch04 7/15/03 4:03 PM Page 196
05 0789729741 ch04 7/15/03 4:03 PM Page 195 CHAPTER 4 Motherboards and Buses 05 0789729741 ch04 7/15/03 4:03 PM Page 196 196 Chapter 4 Motherboards and Buses Motherboard Form Factors Without a doubt, the most important component in a PC system is the main board or motherboard. Some companies refer to the motherboard as a system board or planar. The terms motherboard, main board, system board, and planar are interchangeable, although I prefer the motherboard designation. This chapter examines the various types of motherboards available and those components typically contained on the motherboard and motherboard interface connectors. Several common form factors are used for PC motherboards. The form factor refers to the physical dimensions (size and shape) as well as certain connector, screw hole, and other positions that dictate into which type of case the board will fit. Some are true standards (meaning that all boards with that form factor are interchangeable), whereas others are not standardized enough to allow for inter- changeability. Unfortunately, these nonstandard form factors preclude any easy upgrade or inexpen- sive replacement, which generally means they should be avoided. The more commonly known PC motherboard form factors include the following: Obsolete Form Factors Modern Form Factors All Others ■ Baby-AT ■ ATX ■ Fully proprietary designs ■ Full-size AT ■ micro-ATX (certain Compaq, Packard Bell, Hewlett-Packard, ■ ■ LPX (semiproprietary) Flex-ATX notebook/portable sys- ■ WTX (no longer in production) ■ Mini-ITX (flex-ATX tems, and so on) ■ ITX (flex-ATX variation, never variation) produced) ■ NLX Motherboards have evolved over the years from the original Baby-AT form factor boards used in the original IBM PC and XT to the current ATX and NLX boards used in most full-size desktop and tower systems.
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