Cache Memory, Memory Packaging and Types

CACHE MEMORY

• From French word cacher meaning "to hide"
• Locality principle - When you refer to memory in short intervals, things you need are in the same general area.
• Chunks from slow main memory (Cache Lines) --> Cache (for later)
•  Mean Access Time 
• c = cache access time
• m = memory access time
• h = hit ratio = #times used variable (from Cache) / # times used variable (total)
• Mean Access Time = c + ( 1 - h ) m
• Unified vs. Split Cache
• Unified holds both data AND instructions
• Split --> 1 Cache each 
• allows for parallel access

MEMORY PACKAGING AND TYPES

• Memory Modules
• SIMM = Single Inline Memory Module
• DIMM = Dual Inline Memory Module
• SO-DIMM = Small Outline DIMM (just a smaller DIMM)
• Single or Double Sided ^
• 8 - 16 chips mounted on a board 
• typically about 32 MB/chip