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Memory Hierarchy Technology in Computer Architecture

In this tutorial, we are going to learn about the Memory Hierarchy Technology in Computer Architecture.
Submitted by Uma Dasgupta, on March 04, 2020

Introduction:

In this article, we will discuss the memory hierarchy technology in brief.

Storage devices such as registers, cache main memory disk devices and backup storage are often organized as a hierarchy. The memory technology and storage organization at each level are characterized by five parameters:

1. Access time
2. Memory size
3. Cost per bit or byte
4. Transfer bandwidth
5. Unit of transfer

There are three important properties for maintaining consistency in the memory hierarchy these three properties are Inclusion, Coherence, and Locality.

Information stored in a memory hierarchy satisfies all the above properties the first property i.e the inclusion property, it states as: (M1CM2C...)

The set inclusive implies that all the information's are originally stored in the outermost level Mi and the information word found in Mn then copies of the same word can also be found in all the upper levels Mi+1, Mi+2.

1. Access by word(4 bytes) from a cache block of 32 bytes, such as block A
2. Access by block (32 bytes) from a memory page of 32 blocks or 1 KB such as block B from page B.
3. Access by page 1 KB from a file consisting of many pages like A & B in segment F
4. Segment Transfer with different No. of pages

Coherence Property

The coherence property requires that copies of the same information item at successive memory level should be consistent. If a word is modified in the cache copies of that word must be updated immediately at the higher levels.

There are two strategies for maintaining coherence in a memory hierarchy. The first method is,

1. Write through which demand immediate update through broadcasting Mi+1 level of memory if a word is modified in Mi.
2. Write back – the second method is written which delays the update in Mi.

Locality of references

• Temporal Locality - Recently referenced items like instructions or data are likely to be referred again shortly such as iterative loops process stacks, temporary variables or subroutines.
• Spatial Locality - This refers to the tendency for a process to access items whose addresses are nearer to another for example operations on tables or arrays involve access of a certain clustered area in the address space.
• Sequential Locality - In typical programs the execution of instructions follows a sequential order unless branch instructions create out of order execution. The ratio of in order execution to out of order execution is roughly 5:1 in ordinary programs.

Conclusion:

In this article, we have discussed the different memory hierarchy technology. I hope you all are now clear with what the memory hierarchy technology is? For other queries about the topic please shoot your queries in the comment section below.