To hide the high latencies of DRAM access, modern computer architecture now features a memory hierarchy that besides DRAM also includes SRAM cache memories, typically located on the CPU chip. Memory access first check these caches, which takes only a few cycles. Only if the needed data is not found, an expensive memory access is needed.
Springer-Verlag
L. Liu (Lei) , M. Tamer Özsu
Database Architectures

Boncz, P. (2008). Processor Cache. In L. Liu & M. Tamer Özsu (Eds.), Encyclopedia of Database Systems. Springer-Verlag.