Inside the Machine

N-Way Set Associative Mapping

One way to get some of the benefits of direct-mapped caches while lessening the amount of cache space wasted due to collisions is to restrict the caching of main memory blocks to a subset of the available cache frames. This technique is called set associative mapping, and a few popular implementations of it are described below.

Four-Way Set Associative Mapping

To see an example of what it means to restrict main memory blocks in a subset of available cache frames, take a look at the Figure 11-8, which illustrates four-way set associative mapping.

In Figure 11-8, any of the red blocks can go anywhere in the red set of frames (set 0) and any of the light yellow blocks can go anywhere in the light yellow set of frames (set ...