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Pentium Pro: The First To Handle Over 4 GB Of Memory

Intel's 15 Most Unforgettable x86 CPUs

The Pentium Pro, released in 1995, was the first x86 CPU able to manage more than 4 GB of RAM using Physical Address Extension (PAE), 36-bit address size, and thus 64 GB. An interesting point is that this processor was also the first P6 (the architecture the Core 2 processors are loosely derived from) and also the first x86 to include a Level 2 cache on the processor instead of on the motherboard. In fact, between 256 KB and 1 MB of cache were placed next to the CPU, on the same socket, making the L2 cache on-package as opposed to on-chip, clocked at the same frequency as the CPU.

This processor also had a bit of a performance issue. It ran great in 32-bit applications, but was much slower with software still written in 16 bits (like Windows 95). The cause was simple: access to 16-bit registers caused problems with management of the (32-bit) registers, which canceled out the advantages of the Pentium Pro’s out-of-order architecture.

Intel Pentium Pro
Code name P6
Date released 1995
Architecture 32 bits
Data bus 64 bits
Address bus 36 bits
Maximum memory 64 GB
L1 cache 8 KB + 8 KB
L2 cache external, 256-1024 KB (CPU frequency)
Clock frequency 150-200 MHz
FSB 60-66 MHz
FPU built-in
Fabrication process 600-350 nm
Number of transistors 5,500,000 + cache
Power consumption 29-47 W
Voltage 3.3 V
Die surface area 306-196 mm² + cache
Connector Socket 8

The cache measured 202 mm² (256 KB at 500 nm), 242 mm² (512 KB at 350 nm), or 484 mm² (1 MB at 350 nm). The number of transistors in the cache was 15.5 million (256 KB), 31 million (512 KB), or 62 million (1 MB).

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