Hardware Reference
In-Depth Information
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
Inadditiontotheprocessor/coprocessor,asix-chipsetwasusedtoimplementtheprimary
motherboardcircuitintheoriginalPCandXTsystems.IBMlaterupgradedthistoanine-
chip design in the AT and later systems, mainly by adding more interrupt and DMA con-
troller chips and the nonvolatile Complementary Metal Oxide Semiconductor (CMOS)
RAM/real-time clock chip. All these motherboard chip components came from Intel or
anIntel-licensed manufacturer,excepttheCMOS/clockchip,whichcamefromMotorola.
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 integ-
rate other functions.
In1986,acompanycalled ChipsandTechnologies introducedarevolutionary 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 con-
troller, 8254 system timer, dual 8259 interrupt controllers, dual 8237 DMA controllers,
andevenMC146818CMOS/clockchip.Besidestheprocessor,virtuallyallthemajorchip
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
conceptinPCmotherboardmanufacturing.Notonlydiditgreatlyreducethecostofbuild-
ing a PC motherboard, but it made designing a motherboard much easier. The reduced
