From a practical standpoint the Intel Celeron CPUs have less L1 and L2 cache on them than Intel Pentium CPUs. Same for AMD Duron/Sempron CPUs versus AMD Athlon and newer CPUs. Cache memory is quite expensive in comparison to the same size RAM/Random Access Memory modules but being on the CPU chip itself it is quite fast. Including less cache makes the CPUs cheaper to produce in turn making computers cheaper to buy. They all do the same things, just that those with a greater amount of cache are better to have for working with videos, editing photos, working with large databases and spreadsheets, etc.