Processor Types and Specifications - Upgrading and Repairing PCs - page 112

The main new feature in the fifth-generation Pentium processors was the superscalar ar-
chitecture, in which two instruction execution units could execute instructions simultan-
eouslyinparallel.Laterfifth-generationchipsalsoaddedMMXtechnologytothemix.So
then what did Intel add in the sixth generation to justify calling it a whole new generation
of chip? Besides many minor improvements, the real key features of all sixth-generation
processors are Dynamic Execution and the DIB architecture, plus a greatly improved su-
perscalar design.
Pentium Pro Processors
Intel's successor to the Pentium is called the Pentium Pro. The Pentium Pro was the first
chip in the P6 or sixth-generation processor family. It was introduced in November 1995
and became widely available in 1996. The chip is a 387-pin unit that resides in Socket
8, so it is not pin compatible with earlier Pentiums. The chip is unique among processors
because it is constructed in a multichip module (MCM) physical format, which Intel calls
a dual-cavity PGA package . Inside the 387-pin chip carrier are two dies. One contains the
actual Pentium Pro processor, and the other contains a 256KB, 512KB, or 1MB L2 cache.
(The Pentium Pro with 256KB cache is shown in Figure 3.22 . ) The processor die con-
tains 5.5 million transistors, the 256KB cache die contains 15.5 million transistors, and
the 512KB cache die(s) have 31 million transistors each—for a potential total of nearly
68 million transistors in a Pentium Pro with 1MB of internal cache! A Pentium Pro with
1MB cache has two 512KB cache die and a standard P6 processor die (see Figure 3.23 ) .
The incorporation of L2 cache is one of the most enduring legacies of the Pentium Pro
because this feature has been incorporated into virtually every Intel and AMD processor
built since, with the notable exception of the original Celeron.
Figure 3.22 Pentium Pro processor with 256KB L2 cache. (The cache is on the left side of the processor
die.) Photograph used by permission of Intel Corporation.