Cache memory

Cache (memory) = a very fast (but small size) memory module placed near the CPU

The closeness to the CPU contributes to the access speed of the cache memory !

Cache memory - example

Here is a picture showing a CPU and a cache memory chip side-by-side:

The CPU is on the left and the cache is on the right

Types of cache memories
 

There are 3 types of cache memories:

  1. Level 1 cache memory: (fastest)

      • The cache memory is located on the same silicon material of the CPU itself.

  2. Level 2 cache memory: (2nd fastest)

      • The cache memory is located on a separate silicon material but inside the casing of the CPU silicon material (or within an inch from the CPU)

  3. Level 3 cache memory: (slowest but cheapest)

      • The cache memory is located outside the casing of the CPU silicon material

Important limitation of cache memory
 

  • Due to the speed and distance requirment, the cache memory can "only" be a 0.5 - 2 G bytes

  • FYI:

      • The main memory (RAM) has 4 - 100 G bytes of memory !!!

  • Therefore:

      • The cache memory can only store a portion of the data stored in the main memory

You may wonder how this is possible - we will study the structure of the cache memory soon.