Hardware Reference
In-Depth Information
memory, and other parts.
Table 4.7
lists all the primary chip components used on the original PC/XT
and AT motherboards.
Table 4.7. Primary Chip Components on PC/XT and AT Motherboards
In addition to the processor/coprocessor, a six-chip set was used to implement the primary
motherboard circuit in the original PC and XT systems. IBM later upgraded this to a nine-chip design
in the AT and later systems, mainly by adding more interrupt and DMA controller chips and the
nonvolatile Complementary Metal Oxide Semiconductor (CMOS) RAM/real-time clock chip. All
these motherboard chip components came from Intel or an Intel-licensed manufacturer, except the
CMOS/clock chip, which came from Motorola. Building a clone or copy of one of these IBM systems
required all these chips plus many smaller discrete logic chips to glue the design together, totaling
100 or more individual chips. This kept the price of a motherboard high and left little room on the
board to integrate other functions.
In 1986, a company called Chips and Technologies introduced a revolutionary component called the
82C206—the main part of the first PC motherboard chipset. This was a single chip that integrated all
the functions of the main motherboard chips in an AT-compatible system. This chip included the
functions of the 82284 clock generator, 82288 bus controller, 8254 system timer, dual 8259 interrupt
controllers, dual 8237 DMA controllers, and even MC146818 CMOS/clock chip. Besides the
processor, virtually all the major chip components on a PC motherboard could now be replaced by a
single chip. Four other chips augmented the 82C206 acting as buffers and memory controllers, thus
completing virtually the entire motherboard circuit with five total chips. This first chipset was called
the CS8220 chipset by Chips and Technologies. Needless to say, this was a revolutionary concept in
PC motherboard manufacturing. Not only did it greatly reduce the cost of building a PC motherboard,
but it made designing a motherboard much easier. The reduced component count meant the boards had
more room for integrating other items formerly found on expansion cards. Later, the four chips
augmenting the 82C206 were replaced by a new set of only three chips, and the entire set was called
the New Enhanced AT (NEAT) CS8221 chipset. This was later followed by the 82C836 Single Chip
AT (SCAT) chipset, which finally condensed all the chips in the set to a single chip.
Other chip manufacturers rapidly copied the chipset idea. Companies such as Acer, Erso, Opti,
Suntac, Symphony, UMC, and VLSI each gained an important share of this market. Unfortunately for
many of them, the chipset market has been a volatile one, and many of them have long since gone out
of business. In 1993, VLSI had become the dominant force in the chipset market and had the majority
of the market share; by the next year, VLSI (which later was merged into Philips Semiconductors),
