PC Hardware A Beginner’s Guide

(^60) PC Hardware: A Beginner’s Guide
The 386SL
Intel released the 386SL, which was a 20MHz processor, in 1990. The SL version was
similar to the 386SX, but it was specifically designed for portable computers, featuring
improved power management functions.
Intel 80486DX and SX
Processors did not break the one million-transistor barrier until Intel released the 25MHz
486DX microprocessor in early 1989. This processor had over 1.2 million transistors and
generated 20 MIPS. This processor also introduced a number of innovations, including
the inclusion of processor cache (Level 1 cache) on the processor chip, the introduction of
burst-mode memory access, and for the first time, an integrated math coprocessor. Before
the 486DX, if a user wished to speed up the math functions on a PC, a separate math
coprocessor had to be installed. The 486 was packaged in a 168-pin Ceramic Pin Grid
Assembly (CPGA) package that required a processor-mounted fan to cool it. Processors
before the 486DX had relied on the system fan in the PC’s power supply for cooling.
Asithaddonewiththe386,Intelreleaseda486SXmodelin1991toprovidealow-cost
processor. The primary difference between the DX and the SX models was that the SX
model did not have a built-in math coprocessor.
Intel 80486DX2/DX4
The next model of the 486 was released in 1992 as the 80486DX2. The “2” designation re-
ferred to a technique calledoverclockingthat allows a processor’s clock speed to be doubled.
The DX2 was first released as a 50MHz version, which doubled the DX’s 25MHz bus
speed, and was followed by a 66MHz version (33MHz bus times 2).
The 486DX4 was a product of overclocking as well. The 486 25MHz and 33MHz proces-
sors were overclocked to produce triple their normal clock speeds. This resulted in the DX4
processor available with 75MHz (25MHz times 3) and 100MHz (approximately 33MHz
times 3) clock speeds.
OverclockingistheresultofresettingaPCsoitsmicroprocessorrunsatahigherclock
speed than its manufacturer-specified speed. Although this sounds like it must be illegal,
it is and can be done, especially on Intel processors, because Intel is more conservative in
setting the labeled speed of its processors. If you’d like more information on
overclocking, visit this Web site:www5.tomshardware.com/guides/overclocking/.
AMD 5x86
Intel did not have much competition until Advanced Micro Devices (AMD) released its
75MHz 5x86 microprocessor. The AMD 5x86 processors were compatible with 486 mother-
boards but had similar power to the early Pentium processors.