This document discusses cache memory and its characteristics. It begins by defining cache memory as a small, fast memory located between the CPU and main memory. It then describes the key elements of cache memory, including cache read operations. The document outlines several characteristics of cache memory, such as location, capacity, access methods, and performance metrics. Finally, it discusses different cache memory mapping techniques, including direct mapping, associative mapping, and set associative mapping.

1. CSC 2107– COMPUTER ORGANIZATION
AND ARCHITECTURE
UNIT 6_2
CACHE MEMORY
Bachelors of Science in Computer Science

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 Cache Memory
 What is cache memory
 Cache memory characteristics
 Cache memory mapping techniques
 Virtual memory
Outline

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 At the end of the lecture, students should be
able to:
 Describe cache memory and its uses
 Describe elements and characteristics of cache
memory
 Explain cache memory mapping techniques
 Describe virtual memory and its uses
Learning outcomes
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Cache
 Small amount of fast memory
 Sits between normal main memory and CPU
 May be located on CPU chip or module

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Elements of cache memory

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Cache Read Operation

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Characteristics
 Location
 CPU, Internal and external memory
 Capacity
 Measured in terms of
 Word size
 The natural unit of organisation
 Number of words or Bytes
 Unit of Transfer
 Internal
 Usually governed by data bus width
 External
 Usually a block which is much larger than a word
 Addressable unit
 Smallest location which can be uniquely addressed
 Word internally
 Cluster on M$ disks

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Characteristics
 Access method
 Sequential
 Start at the beginning and read through in order
 Access time depends on location of data and previous location
 e.g. tape
 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
 Random
 Individual addresses identify locations exactly
 Access time is independent of location or previous access
 e.g. RAM
 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

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Characteristics
 Performance
 Access time
 Time between presenting the address and getting the valid data
 Memory Cycle time
 Time may be required for the memory to “recover” before next access
 Cycle time is access + recovery
 Transfer Rate
 Rate at which data can be moved
 Physical type
 Semiconductor
 RAM
 Magnetic
 Disk & Tape
 Optical
 CD & DVD
 Others
 Bubble
 Hologram

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Characteristics
 Physical characteristics
 Decay
 Volatility
 Erasable
 Power consumption
 Organisation
 Physical arrangement of bits into words
 Not always obvious
 e.g. interleaved

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Memory Hierarchy
 Registers
 In CPU
 Internal or Main memory
 May include one or more levels of cache
 “RAM”
 External memory
 Backing store
 Hierarchy List
 Registers
 L1 Cache
 L2 Cache
 Main memory
 Disk cache
 Disk
 Optical
 Tape

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Typical Cache Organization

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Mapping functions
 Cache mapping
 a means for determining which main memory block currently
occupies a cache line
 Three types
 Direct mapping
 Maps each block of main memory into only one possible cache line
 Associative
 Permits each main memory block to be loaded into any line of the
cache
 The cache control logic interprets a memory address
simply as a Tag and a Word field.
 The Tag field uniquely identifies a block of main memory
 Set associative
 The cache consists of number sets, each of which consists of a
number of lines
 Each word maps into all the cache lines in a specific set

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 William Stallings, Computer Organization and
Architecture, 9th Edition
 Chapter 4
Reading list
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Thank you