8. Cache Grows Up

The idea of cache RAM has grown along with the size and complexity of microprocessor chips. A high-end Pentium 4 has 2 Megabytes of cache RAM built into the chip. That’s more than twice the entire memory address space of the original 8088 chip used in the first PC and clones. Putting the cache right on the microprocessor itself removes the slowdown of the wires between chips. You know you are going fast when the speed of light for a few inches makes a difference!

9. Cache Splits Up

As I mentioned above, smaller memories can be addressed faster. Even the physical size of a large memory can slow it down. Microprocessor engineers decided to give the cache memory a cache. Now we have what is known as L1 and L2 cache for level one and level two. The larger and slower cache is L2 and is the usual size quoted in specifications for cache capacity. A few really high-end chips like the Intel Itanium II had three levels of cache RAM.

Beware that the sheer size of cache RAM or the number of layers are not good indications of cache performance. Different microprocessor architectures between Intel and AMD make it especially hard to compare their cache specifications. Just like Intel’s super high clock rates don’t translate into proportionately more performance, doubling of cache size certainly doesn’t double the performance of a microprocessor. Benchmark tests are not perfect, but are a better indicator of microprocessor speed than clock rate or cache size specifications.

Final Words

I hope you enjoyed this first installment of the history of microprocessors. It’s nice to know the humble beginnings and compare them to how far we have come in the computing capability of a CPU. Understanding the basics of how a microprocessor works gives you a leg-up on grokking the more advanced features of today’s Mega-microprocessors.

In future installments, we are going to dig into such microprocessor enhancements as super-scalar, hyper-threading and dual core. The concepts aren’t that hard and in the end you can boast about the latest features of your new computer with confidence.

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