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Integrated Level 2 Cache

The Intel Pentium Pro processor comes with an integrated level 2 cache. The "chip" that you plug into the motherboard is really two chips. One is the processor itself (including the level 1 cache) and the other is the level 2 cache. These processors are available with 256 KB, 512 KB and 1 MB of level 2 cache. This is a very performance-enhancing design, because it allows the level 2 cache to run at the processor's internal speed (usually 180 or 200 MHz) instead of just the system bus speed (60 or 66 MHz). It also gives you one less thing to worry about in setting up a new system, because all of the support circuitry, tag RAM etc., is inside the chip.

One drawback of this design is that it is not possible to increase the level 2 cache without replacing the processor. These processors are also very expensive due to the difficulty of manufacturing the large chip required for the level 2 cache. Regular cache is made of many small chips, whereas this one is made from one large chip. In addition, defects in the level 2 cache often are not discoverable until after the processor and cache are put into their shared package; this means the processor has to be discarded as well if a defect is found in the cache chip. This is the main reason that Intel moved away from putting integrated cache on its Pentium II processor. No other CPUs currently use this design and it is unlikely that any more ever will.

The integrated level 2 cache of the Pentium Pro is also faster than the older cache used with fifth generation systems due to performance enhancements. The main one is that the cache is transactional, or non-blocking.

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