Intro to cache memory

Intro to cache memoryKosarev NikolayMIPT Nov, 2009Agenda

Cache

Placement of cache block

Searching of data in the cache

Replacement policies

Write policies

CacheCache is a buffer for storing of data copies for rapid access

Takes advantage of the principle of locality (temporal, spatial)

Consists of blocks / lines (portions of data retrieved from the main memory)

Each block has an address tag (address of the block in the main memory)

Hit (Miss) – data was found (wasn’t found) in the cache

Placement of cache block3 types of cache

Direct mapped: (block address) mod (blocks in cache)

Set associative: (block address) mod (sets in cache)

Fully associative

2-way set associative cacheSearching of dataProcessor address is analyzed

Index field selects the set

Tag is compared against all blocks in set for a hit

Offset field selects data from the block

Note: all address tags are searched in parallel

Cache HIT access time is critical

Replacement policies3 frequently used algorithms

Random

Simple to implement

Least recently used (LRU)

Block unused for the longest time is replaced

Complicated to calculate -> approximated

First in first out (FIFO)

The oldest block is replaced