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COMPUTER ORGANIZATION & ARCHITECTURE
Van-Khoa Pham (PhD.)

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Chapter 4
Cache Memory

Location
Internal (e.g. processor registers, cache,
main memory)
External (e.g. optical disks, magnetic disks,
tapes)
Capacity
Number of words
Number of bytes
Unit of Transfer
Word
Block
Access Method
Sequential
Direct
Random
Associative

Performance
Access time
Cycle time
Transfer rate
Physical Type
Semiconductor
Magnetic
Optical
Magneto-optical
Physical Characteristics
Volatile/nonvolatile
Erasable/nonerasable
Organization
Memory modules

Table 4.1
Key Characteristics of Computer Memory Systems

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Characteristics of Memory Systems
 Location
 Refers to whether memory is internal and external to the computer
 Internal memory is often equated with main memory
 Processor requires its own local memory, in the form of registers
 Cache is another form of internal memory
 External memory consists of peripheral storage devices that are accessible to the processor

via I/O controllers

 Capacity
 Memory is typically expressed in terms of bytes

 Unit of transfer
 For internal memory the unit of transfer is equal to the number of electrical lines into and out of

the memory module

Method of Accessing Units of Data
Sequential
access

Direct
access

Random
access

Memory is organized into
units of data called
records

Involves a shared readwrite mechanism

Each addressable
location in memory has a
unique, physically wiredin addressing mechanism

A word is retrieved
based on a portion of its
contents rather than its
address

Access must be made in
a specific linear
sequence

Individual blocks or
records have a unique
address based on
physical location

The time to access a
given location is
independent of the
sequence of prior
accesses and is constant

Each location has its own
addressing mechanism
and retrieval time is
constant independent of
location or prior access
patterns

Access time is variable

Access time is variable

Any location can be
selected at random and
directly addressed and
accessed

Cache memories may
employ associative
access

Main memory and some
cache systems are
random access

Associative

Capacity and Performance:
The two most important characteristics of
memory
Three performance parameters are used:
Access time (latency)
•For random-access memory it is the
time it takes to perform a read or
write
...
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...e tag entry at that page location (Location 300) to
determine if the information is in the cache (a hit).
 The CPU receives the data in reduced wait states if a hit.

© 2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

Main memory address (binary)
Tag
(hex)

Tag

Line + Word

00
00

000000000000000000000000
000000000000000000000100

00
00

000000001111111111111000
000000001111111111111100

Data
13579246

Line
Data
Number
13579246 0000
11235813 0001

16
16

000101100000000000000000
000101100000000000000100

77777777
11235813

Tag
00
16

16

000101100011001110011100

FEDCBA98

16

FEDCBA98

0CE7

16

000101101111111111111100

12345678

FF
16

11223344
12345678

3FFE
3FFF

8 bits

32 bits

FF
FF

111111110000000000000000
111111110000000000000100

FF
FF

111111111111111111111000
111111111111111111111100

16-Kline cache

11223344
24682468

Note: Memory address values are
in binary representation;
other values are in hexadecimal

32 bits
16-MByte main memory

Tag

Line

Word

8 bits

14 bits

2 bits

Main memory address =

Figure 4.10 Direct Mapping Example

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Single Processor

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Mapping Cache Size
Direct
MAPPING

Fully-associative

Set-associative
2-way set-associative

4 KB
8 KB
CACHE
SIZE

CACHE
SETS

4-way set-associative

16 KB
32 KB

8-way set-associative

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Mapping Cache Size

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Mapping Cache Size

CPU yêu cầu
tìm block số 6

Bộ nhớ Cache đọc
yêu cầu của CPU
Thông báo không
tìm thấy trong
Cache
Cache gửi yêu cầu
của CPU xuống
BUS
BUS gửi yêu cầu của
CPU xuống bộ nhớ
Bộ nhớ chính gửi
chính
block số 6 lên Cache
và CPU

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Mapping Cache Size

CPU yêu cầu
tìm block số 6
Bộ nhớ Cache đọc
yêu cầu của CPU
Thông báo tìm thấy
block số 6 trong
Cache

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Mapping Cache Size

CPU yêu cầu
tìm block số
619

Bộ nhớ Cache đọc
yêu cầu của CPU

Bộ nhớ chính gửi block
số 619 lên Cache và
CPU

Thông báo không
tìm thấy trong
Cache
Cache gửi yêu cầu
của CPU xuống
BUS
BUS gửi yêu cầu của
CPU xuống bộ nhớ
chính

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Mapping Cache Size

Thông tin cho
từng mức
Cache
Thông tin cho cả
hệ thống Cache

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Mapping Cache Size

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Mapping Cache Size

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Mapping, Cache Size and
Replacement Policy

16

BLOCK
IN
CACHE

32

64

2-way

4 KB
8 KB
16 KB
32 KB

set-

associative
CACHE
SIZE

CACH
E SETS
4-way

set-

associative

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Mapping, Cache Size and
Replacement Policy

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Mapping, Cache Size and
Replacement Policy