PC Hardware in a Nutshell, 3rd Edition

Intel Processors

Nearly all current PCs use either an Intel CPU or an Intel-compatible AMD Athlon CPU. The dominance of Intel in CPUs and Microsoft in operating systems gave rise to the hybrid term Wintel, which refers to systems that run Windows on an Intel or compatible CPU. Intel processors are referred to generically as x86 processors, based on Intel’s early processor naming convention, 8086, 80186, 80286, etc. Intel has produced seven CPU generations, the first five of which are obsolete and the sixth obsolescent. They are as follows:

First generation

The 8086 was Intel’s first mainstream processor, and used 16 bits for both internal and external communications. The 8086 was first used in the late 1970s in dedicated word processors and minicomputers such as the DisplayWriter and the System/23 DataMaster. When IBM shipped its first PC in 1981, it used the 8088, an 8086 variant that used 16 bits internally but only 8 bits externally, because 8-bit peripherals were more readily available and less expensive then than were 16-bit components. The 8086 achieved prominence much later when Compaq created the DeskPro as an improved clone of the IBM PC/XT. A few early PCs, notably Radio Shack models, were also built around the 80186 and 80188 CPUs, which were enhanced versions of the 8086 and 8088 respectively. The 8088 and 8086 CPUs did not include an FPU, although an 8087 FPU, called a math coprocessor, was available as an optional upgrade chip. First generation Intel CPUs (or their modern equivalents) are still used in some embedded applications, but they are long obsolete as general-purpose CPUs.

Second generation

In 1982, Intel introduced the long-awaited follow-on to its first generation processors. The 80286, based on the iAPX-32 core, provided a quantum leap in processor performance, executing instructions as much as five times faster than an 808x processor running at the same clock speed. The 80286 processed instructions as fast as many mainframe processors of the time. The 80286 also increased addressable memory from 1 MB to 16 MB, and introduced protected mode operations. The IBM PC/AT was the first commercial implementation of the 80286. The optional 80287 FPU chip added floating-point acceleration to 80286 systems. Although long obsolete as a general-purpose CPU, the 80286 is still used in embedded controllers.

Third generation

Intel’s next generation debuted in 1985 as the 80386, later shortened to just 386. The 386 was Intel’s first 32-bit CPU, which communicated internally and externally with a 32-bit data bus and 32-bit address bus. The 386 was available in 16, 20, 25, and 33 MHz versions. Although 386 clock speeds were only slightly faster than those of the 80286, improved architecture resulted in significant performance increases. The optional 80387 FPU added floating-point acceleration to 386 systems. Intel later renamed the 386 to the 386DX and released a cheaper version called the 386SX, which used 32 bits internally but only 16 bits externally. The 386SX was notable as the first Intel processor that included an internal (L1) cache, although it was only 8 KB and relatively inefficient. The 386 is long obsolete as a general-purpose CPU, but it is still commonly used in embedded controllers.

Fourth generation

Intel’s next generation debuted in 1989 as the 486 (there never was an 80486). The 486 was a full 32-bit CPU with 8 KB of L1 cache, included a built-in FPU, and was available in speeds from 20 MHz to 50 MHz. Intel released 486DX and 486SX versions. The 486SX was in fact a 486DX with the FPU disabled. Intel also sold the 487SX, which was actually a full-blown 486DX. Installing a 487SX in the coprocessor socket simply disabled the existing 486SX. The 486DX/2, introduced in 1992, was the first Intel processor that ran internally at a multiple of the memory bus speed. The 486DX/2 clock ran at twice bus speed, and was available in 25/50, 33/66, and 40/80 MHz versions. The 486DX/4, introduced in 1994, ran (despite its name) at thrice bus speed, doubled L1 cache to 16 KB, and was available in 25/75, 33/100, and 40/120 versions. The 486 is obsolete as a general-purpose CPU, although it is still popular in embedded applications.

Fifth generation

The Intel Pentium CPU defines the fifth generation. It provides much better performance than its 486 ancestors by incorporating several architectural improvements, most notably an increase in data bus width from 32 bits to 64 bits and an increase in CPU memory bus speed from 33 MHz to 60 and 66 MHz. Intel actually shipped several different versions of the Pentium, including:

• Pentium P54—the original Pentium shipped in 1993 in 50, 60, and 66 MHz versions using a 1X CPU multiplier, ran (hot) at 5.0 volts, contained a dual 8 KB + 8 KB L1 cache, and fit Socket 4 motherboards.

• Pentium P54C—the “Classic Pentium” first shipped in 1994, was available in speeds from 75 to 200 MHz using CPU multipliers from 1.5 to 3.0, used 3.3 volts, and contained the same dual L1 cache as the P54. P54C CPUs fit Socket 5 motherboards and most Socket 7 motherboards.

• Pentium P55C—the Pentium/MMX shipped in 1997, was available in speeds from 166 to 233 MHz, using CPU multipliers from 2.5 to 3.5, used 3.3 volts, and contained a dual 16 KB + 16 KB L1 cache, twice the size of earlier Pentiums. The other major change from the P54C was the addition of the MMX instruction set, a set of additional instructions that greatly improved graphics processing speed. P55C CPUs fit Socket 7 motherboards, and are still in limited distribution as of July 2003.

The Pentium and other fifth-generation processors are obsolete, although millions of Pentium systems remain in service. Any system that uses a fifth-generation processor is too old to upgrade economically.

Sixth generation

This generation began with the 1995 introduction of the Pentium Pro, and includes the Pentium II, Celeron, and Pentium III processors. Late sixth-generation Intel desktop processors had been relegated to entry-level systems by early 2002 and had been discontinued as mainstream products by mid-2002. By late 2002, only the Tualatin-core Celeron processors remained as representatives of this generation. Although it is still technically feasible to upgrade the processor in many sixth-generation systems, in practical terms it usually makes more sense to replace the motherboard and processor with seventh-generation products.

Seventh generation

This is the current generation of Intel processors, and includes Intel’s flagship Pentium 4 as well as various Celeron processors based on the Pentium 4 architecture.

Intel currently manufactures several sixth-generation processors, including numerous variants and derivatives of the Celeron and Pentium III, and two seventh-generation processors, the Pentium 4 and the Celeron. The following sections describe current and recent Intel processors.

Tip

There are times when it is essential to identify the processor a system uses. For information about identifying Intel processors, see http://www.hardwareguys.com/supplement/cpu-id.html.