The TLB is a piece of very fast, associative memory, capable of searching many areas of memory simultaneously. This means that many table entries can be searched at the same time for a logical-page entry. This type of memory is very expensive which means that not much of it is used; MMUs usually use TLBs with between 64 and 1024 entries.

The TLB fills up with recent searches when a search is not successful, the entries are added. TLBs store only part of a page table's entries, because the memory is expensive and limited.

A new page table causes all the entries stored in the TLB to become useless. When a new page table is used for example, on a context switch the TLB entries must be erased to make sure the new process's logical-address space maps to the old process's physical-address space.