PC Hardware in a Nutshell, 3rd Edition

Pentium Pro processor architecture

Although the Pentium Pro is obsolete, it was the first Intel sixth-generation processor, and as such introduced many important architectural improvements. Understanding the Pentium Pro vis-à-vis the Pentium will help you understand current Intel CPU models. The two CPUs differ in the following major respects:

Secondary (L2) cache

Pentium-based systems may optionally be equipped with an external L2 secondary cache of any size supported by the chipset. Typical Pentium systems have a 256 KB L2 cache, but high-performance motherboards may include a 512 KB, 1 MB, or larger L2 cache. But Pentium L2 caches use a narrow (32-bit), slow (60 or 66 MHz memory bus speed) link between the processor’s L1 cache and the L2 cache. The Pentium Pro L2 cache is internal, located on the CPU itself, and the Pentium Pro uses a 64-bit data path running at full processor speed to link L1 cache to L2 cache. The dedicated high-speed bus used to connect to cache is called the Backside Bus (BSB), as opposed to the traditional CPU-to-chipset bus, which is now designated the Frontside Bus (FSB). In conjunction, the BSB and FSB are called the Dual Independent Bus (DIB) architecture. DIB architecture yields dramatically improved cache performance. In effect, 256 KB of Pentium Pro L2 cache provides about the same performance boost as 2 MB or more of Pentium L2 cache.

Dynamic execution

The Pentium Pro uses a combination of techniques—including branch prediction, data flow analysis, and ...