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Starting with the Pentium II processor (a.k.a. "Klamath") Intel has introduced a new form of packaging, called SEC (Single Edge Contact). The integrated cache of the Pentium Pro processors ran at processor speed and offered very high performance, but was very expensive to manufacture. The motherboard cache of the regular Pentium was easy and cheap to produce but offered lower performance. SEC is a compromise where the processor and cache are mounted together on a small "daughterboard" that plugs into the motherboard. This greatly reduces manufacturing costs, and also means that a bad cache chip doesn't result in the processor being wasted.
This type of cache runs at a faster speed than it would if it were on the motherboard, but slower than an integrated cache; this is why it is a compromise between the other two designs. On the Pentium II the level 2 cache runs at half the processor speed. So a 266 MHz Pentium II will have a 133 MHz level 2 cache. Not as good as the 200 MHz Pentium Pro's integrated cache, but a lot faster than running it at 66 MHz. The Pentium II's cache is also non-blocking, like the Pentium Pro's.
Note: Even though the
Pentium II has an architecture very similar to that of the Pentium Pro, due to a design
limitation it will only cache the first 512 MB of system memory. The Pentium Pro will
cache up to 4 GB of system memory.
Next: Motherboard Cache