PC Hardware in a Nutshell, 3rd Edition

Pentium Pro

Intel’s first sixth-generation CPU, the Pentium Pro, was introduced in November 1995—along with the new 3.3 volt 387-pin Socket 8 motherboards required to accept it—and was discontinued in late 1998. Pentium Pro processors are no longer made, but remain available on the used market. Intel positioned the Pentium Pro for servers, a niche it never escaped, and where it continued to sell in shrinking numbers until its replacement, the Pentium II Xeon, shipped in mid-1998. The Pentium Pro predated the P55C Pentium/MMX, and never shipped in an MMX version. The Pentium Pro never sold in large numbers for two reasons:

Cost

The Pentium Pro was a very expensive processor to build. Its core logic comprised 5.5 million transistors (versus 4.1 million in the P55C), but the real problem was that the Pentium Pro also included a large L2 cache on the same substrate as the CPU. This L2 cache required millions of additional transistors, which in turn required a much larger die size and resulted in a much lower percentage yield of usable processors, both factors that kept Pentium Pro prices very high relative to other Intel CPUs.

32-bit optimization

The Pentium Pro was optimized to execute 32-bit operations efficiently at the expense of 16-bit performance. For servers, 32-bit optimization is ideal, but slow 16-bit operations meant that a Pentium Pro actually ran many Windows 95 client applications slower than a Pentium running at the same clock speed.

The Pentium Pro shipped in 133, 150, ...