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William Stallings
Computer Organization
and Architecture
7th Edition


Cache Memory

1.Characteristics:
a. Location
b. Capacity
c. Unit of transfer
d. Access method
e. Performance
f. Physical type
g. Physical characteristics
h. Organisation

2.Location
a. CPU
b. Internal
c. External

3.Capacity
a. Word size
-The natural unit of organisation
b. Number of words
- or Bytes

4.Unit of Transfer
a. Internal
- Usually governed by data bus width
b. External
- Usually a block which is much larger than a word
c. Addressable unit
- Smallest location which can be uniquely addressed
- Word internally

5.Access Methods (1)
a. Sequential
- Start at the beginning and read through in order
- Access time depends on location of data and previous location
- e.g. tape
b. Direct
- Individual blocks have unique address
- Access is by jumping to vicinity plus sequential search
- Access time depends on location and previous location
- e.g. disk

6.Access Methods (2)
a. Random
- Individual addresses identify locations exactly
- Access time is independent of location or previous access
- e.g. RAM
b. Associative
- Data is located by a comparison with contents of a portion of the store
- Access time is independent of location or previous access
- e.g. cache

7.Memory Hierarchy
a. Registers
- In CPU
b. Internal or Main memory
- May include one or more levels of cache
- “RAM”
c. External memory
- Backing store

8.Memory Hierarchy - Diagram

9.Performance
a. Access time
- Time between presenting the address and getting the valid data
b. Memory Cycle time
- Time may be required for the memory to “recover” before next access
- Cycle time is access + recovery
c. Transfer Rate
- Rate at which data can be moved