Memory Hierarchy

CPU Speed is dominated by memory performance

-More significant than : ISA, circuit optimization, pipelining, etc

Trick 1: Make slow main memory appear faster (caching)
Trick 2: Make small main memory appear bigger(virtual memory)

Memory Hierarchy Levels

Block(aka line): unit of copying
-may be multiple words
If accessed data is present in upper level
-access satisfied by upper level

If accessed data is absent

-miss-->block copied from lower level
-then accessed data is supplied from upper level

Parking Lot Analogy

Suppose we have 1000 parking spots. However, instead of being unnumbered, each parking spot is given a 3 digit number from 000 to 999.

Your parking spot is based on the first 3 digits of your student ID number.

What problem can occur? If you received your social security number (student ID) in Maryland, the first three digits of your student ID is likely to be in the low 200's.

Thus, there's a much higher chance someone will be in your parking spot. There's also a chance that parking spots numbered in the 900's might be mostly empty since few students may have student IDs with the first 3 digits in that range.

This is basically the direct-mapped scheme. The advantages of this scheme are that it's simple to find your parking spot. It can only be in one location.