- a Blocking Cache will not accept any more request until the miss is taken care of.
- a Non-blocking cache will accept further requests and try to service those requests. Now the additional requests may also hit or miss. A "hit-under-X-misses" cache will allow X number of misses to be outstanding in the cache before blocking. For example, a"hit-under-2-misses" cache will keep running if there are at most 2 misses that still not complete. If additional requests are hit, the cache will keep working. However, if a request is a third miss, the cache will block (stop receiving requests).
vis:https://www.quora.com/What-is-meant-by-non-blocking-cache-and-multi-banked-cache