2.36 What does the "chip set" do?
Description
This item is from the PC Hardware FAQ, by Willie Lim and Ralph Valentino with numerous contributions by others. (v1.25).
2.36 What does the "chip set" do?
[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]
The motherboard "chip set" contains all the logic that's not in the microprocessor ("uP") and its coprocessor, or the memory. These functions always include:
* Address decoding and "memory mapping" * keyboard interface controller (which includes reset generator) * Direct Memory Access (DMA) channels * interrupt controller * bus controller(s) * battery-powered "real time" clock/calendar circuit * crystal-controlled clock oscillator(s) * main memory controllerThey almost always include:
* controller for cache external to the uP * "turbo" switch logic * programmable "wait state" logic
and some of them include:
* controller(s) for PCMCIA slots * "green" power-conservation logic * video display logic for CRT, LCD, or both * serial ports, parallel ports, floppy, SCSI and/or IDE, etc. controllers * network interface controllers (for Ethernet)
Some people consider the BIOS ROM part of the "chip set."
Sometimes part of an EISA or VLB bus controller is implemented in an optional, socketed integrated circuit. A motherboard like that can be sold with the socket empty, and you have to go back and buy the "bus mastering option" later when you find out you need it.
"Chip sets" are usually a set of highly integrated, special purpose integrated circuits. The keyboard interface controller is usually in a 40-pin dual-inline pin (DIP) package compatible with the Intel 8048 single-chip microcomputer which was used for that function in the IBMPC-AT. The rest of the logic often fits in a single IC. In the trade, you may see this single IC referred to as "the chipset," even though the keyboard interface and other logic is external. The Asian data sheets often call the high-integration chips "LSIs."
The word "ChipSet" is a trademark of Chips and Technologies Inc. (San Jose, California), which introduced a 5-chip set of LSIs for AT-clone motherboards in early 1985. CTI may also own "chipset" and "Chipset"; I don't know. CTI was very successful at promoting the term "ChipSet," but less successful at associating it in the public mind with their particular brand. People use the word to refer to any high integration chip used in PCs. For example, you'll hear people talk about the "ET4000 video chipset." The ET4000 is a single chip which integrates most of an SVGA controller. The word "ASIC" (application-specific integrated circuit) would be more appropriate.
Single, high-integration ICs are not very good at driving heavily loaded signals, like the ones in the memory array and the expansion slots. Better motherboards use buffer chips external to the LSI for this electrical function. It may not show up in "WinMark" comparisons, but it shows in electrical compatibility. Well-buffered motherboards are less likely to require SIMM "cherry-picking," and are more likely to work at high ambient temperatures. The 74F245, which costs about 15 cents in high volume, is often used for this electrical buffering.
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