Short for Level 2 cache, L2 cache, secondary cache, or external cache, L2 is specialized, high-performance computer memory on the die of the CPU (central processing unit). Unlike Layer 1 cache, L2 cache was on the motherboard on earlier computers, although with newer processors it is found on the processor chip. It's located closer to the CPU, and therefore has lower latency, than the L3 cache.
The L2 cache is on the same processor chip and same die as the CPU. It requires close proximity to the CPU to achieve maximum performance. However, it is not technically part of the CPU.
L2 cache was first introduced with the Intel Pentium and Pentium Pro computers and included with every subsequent processor, except some versions of the Celeron processor. L2 cache isn't as fast as the L1 cache, but is only slightly slower since it's still on the same processor chip, and is still faster than the computer's memory. The L2 cache is the second thing the computer looks at when performing instructions.