The Early Intel CPUs

The table below lists specifications for some early CPUs made by Intel. Until the introduction of Pentium chips and their clones, most chips were rated by the criteria listed in this table.

The 80386SX chip had a smaller path size than the 80386DX, although it was developed later.

At the time Intel first manufactured the 80386DX with its 32-bit path size, system-board manufacturers could produce at a reasonable cost a systemboard with a path size of only 16 bits, or 2 bytes. Therefore, the system-board manufacturers could not take advantage of the DX’s 32-bit path size and chose not to use the first 80386DX chips.

In response to this, Intel produced the cheaper 80386SX chip, which accommodated the smaller path size and kept the cost of the system more reasonable for personal computer users.

The 80386SX chip used an internal 32-bit word size but an external 16-bit path size. (Internal refers to operations inside the CPU, and external refers to operations between the inside and outside of the CPU, such as those on the bus.) The smaller path size of the 80386SX is the reason that it is slower than the 80386DX chip (S stands for single and D for double).

The table above lists the earlier CPUs chronologically, based on their introduction in the marketplace.

If you look at one of these CPUs, you see it is labeled as 80386SX-16, 80486DX2-50, or another number using a similar convention. The number at the end of the model number, 16 or 50 in the examples, refers to the speed of the CPU in megahertz.

The 2 following the 486DX CPU indicates that the chip can work in overdrive mode, which doubles the external clock speed to increase the overall speed of the computer.

Coprocessors

Some older CPU microchips were designed to work hand in hand with a secondary microchip processor called a coprocessor.

The coprocessor performed calculations for the CPU at a faster speed than the CPU could.

The coprocessor for the 80386 chip is the 80387. The 486DX has the coprocessor built into the CPU housing.

The 486SX has the coprocessor portion of the chip disabled. Software must be written to make use of a coprocessor.

Most software today assumes you have a 486DX or Pentium chip and writes its code to take advantage of this coprocessor capability.

The Pentium CPU

The latest CPU microchips by Intel are the Pentium series of chips. A Pentium chip has two arithmetic logic units, meaning that it can perform two calculations at the same time; it is therefore a true multiprocessor. Pentiums have a 64-bit external path size and two 32-bit internal paths, one for each arithmetic logic unit.

Comparing Chips

To compare the Pentium family of chips and the Pentium competitors, you need to understand bus speed, processor speed, multiplier, and memory cache.

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