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[ The PC Guide | Systems and Components Reference Guide | The Processor | Processor Architecture and Operation | External Processor Interfaces and Operation ]

Dedicated "Backside" Cache Bus

Conventional processors use level 2 cache on the motherboard and connect to it using the standard memory bus arrangement. To achieve better performance, many newer processors use a dedicated high-speed bus to connect the processor to the level 2 cache. For example, the standard Pentium 200 runs on a 66 MHz system bus, and the system cache runs at this speed as well, but the Pentium Pro 200 has an integrated level 2 cache that runs at full processor speed--200 MHz.

A special backside bus manages this high-speed data link between the processor and the level 2 cache (which is entirely within the Pentium Pro package, since it contains both the processor and level 2 cache). The Pentium II processor has a compromise arrangement that is similar; it runs at half the processor speed, so a 266 MHz Pentium II runs its cache bus at 133 MHz (much slower than the Pentium Pro but much faster than the Pentium). Both of these buses are transactional (non-blocking) so they allow for concurrent requests to the system cache, greatly improving performance.

Another advantage of this design is that having separate caches and buses to run them is far superior for multiprocessing. Not only does each processor have its own cache without having to share a single one on the motherboard, each cache has an independent, non-interfering bus to service it.

Note: Intel calls the use of a separate bus for the cache and memory Dual Independent Bus (DIB) architecture.

Next: Processor / Memory Data Bus

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