The
Pentium Pro was the immediate successor to the
Pentium processor. Unfortunately, the
manufacturing cost of the Pentium Pro was
excessive due to the fact that you had to mount both the processor and cache dies in the same package. Since packaging dies is an
error prone process, the probablity of
failure was doubled; if either the CPU die or the cache die were
defective, the entire package had to be
tossed.
Intel learned this lesson and started putting the cache and processor in separate packages with the Pentium II; this processor simply has both on a PC board which then plugs into a slot; the Slot 1 to be precise. This does not come without penalty, though; the cache had to be run at half the speed of the die. Synchronization was an issue, due to the longer traces between the CPU and cache.
This problem has since been solved by putting the cache on the same die as the CPU; the Pentium III coppermine flipchip is of this type. 256K of screaming-fast-cache right on the same chip as the processor. Murr.