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COMPUTER SYSTEM ARCHITECTURE CACHE MEMORY - Coggle Diagram
COMPUTER SYSTEM ARCHITECTURE CACHE MEMORY
INTRODUCTION
INTRODUCTION
There is no technology that is optimal in satisfying the memory requirements for a computer system
INTRODUCTION
Internal memory
: Directly accessible by the processor
External memory
:Accessible by the processor via an I/O Module
MEMORY HIERARCHY
MEMORY HIERARCHY
The term memory hierarchy is used in the theory of computation when discussing performance issues in computer architectural design
Key characteristic of memory:
:Capacity
:Access time
:Cost
As one goes down the hierarchy, the following
occur:
:Decreasing cost per bit
:Increasing capacity
:Increasing access time
:Decreasing frequency of accessing memory by the
processor
CACHE MEMORY
CACHE MEMORY : :Cache is internal memory :Cache contains a copy of portions of main
memory
:The larger the cache, the larger the number of gates involved in addressing the cache. :Cache memory is random access memory(RAM) that a computer microprocessor can access more quickly than it can access regular RAM.
HOW IT WORKS
The CPU looks for data first in the cache, and if the data is not found there, it looks in main memory.
CPU
CACHE
RAM
Mapping functions
Because there are fewer cache lines than main memory blocks an algorithm is needed for mapping main memory block into cache line
Mapping Techniques
There are 3 techniques for mapping : Direct mapping
Associative mapping
Set Associative mapping
Direct Mapping
The content of location in main memory can be stored at one on and only one specific location in the cache ( it mapped to exactly one location in the cache) If the CPU request the contents of a specific memory location, there is only one block in the cache that could possibly contain that
information
Main Disavantage : There is a fixed cache location for any given block Thus if a program happens to reference words Thus if a program happens to reference words same line, the block will be continuously swapped in the cache, the hit ratio will be low.
Cache hit : Data found in cache. Results in data transfer at maximum speed.
Associative Mapping
Overcomes the disadvantage of direct mapping by permitting each main memory block to be loaded into any line of the cache. There is flexibility as to which block to replace There is flexibility as to which block to replace
Disadvantage:
The complex circuitry require
Examine the tag of all cache lines in parallel
Set Associative Mapping
Set Associative Mapped Cache combines the ideas of Direct Mapped and Associative cache.
Set-associative mapping allows that eachword that is present in the cache can have twoor more words in the main memory for thesame index address