- Main memory typically GBs
- Accessing main memory takes 100s of cpu cycles!!!
- To avoid the main memory bottleneck:
- Copies of recently used data and instructions are held in smaller memories with high speed access, e.g.
- L1 cache (typically data and instruction caches)
- L2 cache, larger and slower than L2
- L3 cache, larger and slower than L3
- Number, size and speed of caches varies with processor
Important: when cache makes a copy of data it simultaneously copies a chunk of data from consecutive memory addresses.