(L1 cache, level one cache) A small, fast cache memory inside or close to the CPU chip.

For example, an Intel 80486 has an eight-kilobyte on-chip cache, and most Pentiums have a 16-KB on-chip level one cache that consists of an 8-KB instruction cache and an 8-KB data cache.

The larger, slower secondary cache is normally connected to the CPU via its external bus.