The idea of cache memory is primarily based on:

The idea of cache memory is primarily based on the principle of locality. This principle is divided into two parts: temporal locality and spatial locality.

1. Temporal Locality: This refers to the concept that a resource that was needed recently will be needed again in the near future. In terms of cache memory, if a data or instruction is used, there is a high probability that it will be used again soon. Therefore, it is kept in the cache memory to reduce the time it would take to fetch it from the main memory.

2. Spatial Locality: This refers to the concept that the likelihood of referencing a resource is higher if a resource near it was just referenced. In terms of cache memory, if a data or instruction is used, there is a high probability that the data or instruction near it will be used soon. Therefore, blocks of data around it are also loaded into the cache memory.

In summary, the idea of cache memory is to store frequently used data or instructions to make them quickly accessible, thereby improving the overall speed and performance of the computer system.