Multiple input two-level cache directory with mini-directory for initial comparisons and main directory for mini-directory misses

A method for operating a cache directory that compares N read cache tags against X stored cache tags to determine whether each of the N read cache tags matches one of the X stored cache tags, wherein N is greater than one, the method including the steps of:

• (a) storing the X stored cache tags in a main directory;
• (b) storing a subset of the X stored cache tags in a mini-directory, the subset including M stored cache tags, M being at least as large as N and less than X;
• (c) comparing at least two of the N read cache tags against the M stored cache tags in the mini-directory simultaneously;
• (d) indicating that each of the N read cache tags that matches one of the M stored cache tags matches one of the X stored cache tags;
• and
• (e) when at least one of the N read cache tags does not match any of the M stored cache tags, comparing the at least one of the N read cache tags against the X stored cache tags in the main directory.

A cache directory, associated with a cache memory, that stores X cache tags and responds to N read cache tags in a single cache directory access to provide a corresponding cache block index for each of the N read cache tags, wherein N is greater than one, each cache tag corresponding to a block of cache data, the cache memory storing X blocks of cache data, the block index provided by the cache directory for each one of the N read cache tags identifying a location in the cache memory wherein the block of cache data corresponding to the one of the N read cache tags is stored, the cache directory including:

• a mini-directory that stores M cache tags that are a subset of the X cache tags, M being equal to at least N, the mini-directory being fully associative and simultaneously comparing each of the M stored cache tags against each of the N read cache tags, the mini-directory providing a corresponding block index for each one of the M stored cache tags that matches at least one of the N read cache tags;
• a main directory that stores the X cache tags, the main directory being fully associative and comparing P read cache tags against each of the X cache tags simultaneously, P being less than N, the main directory providing a corresponding block index for each one of the X stored cache tags that matches one of the P read cache tags;
• and
• control means for initially comparing the N read cache tags against the mini-directory to provide a block index for each of the N read cache tags that hits in the mini-directory, and for comparing each of the N read cache tags that misses in the mini-directory against the main directory to provide a block index for each.