Main Memory of Computer

Learning Objectives

To realize:

1.The needs of computer memory

2.Memory sizes of computer

3.Types of memory

4.Main memory

Introduction to computer memory

Comparison between human and

computer memory

Role Play:

If you can now choose your brain memory, what would you choose:

1)Large storage with low speed

2)Small storage with high speed

3)Large storage with high speed

$300

$500

$1000

Basic Memory Units

Binary representation is used to

represent all data and instructions

in computer

8bits = 1byte = word symbol

1KB(Kilobyte) = 1024B

1MB(Megabyte) = 1024KB

1GB(Gigabyte) = 1024MB

Memory Sizes

The size of the main memory is measured in kilobytes (KB),which is equal to 1024 bytes. For convenience,we sometimes round off the value of K to 1000.For example,640 KB is approximately 640 000 bytes (640 x 1000).To measure memory of large sizes,we use megabytes (MB) and gigabytes (GB).1 MB = 1024 KB = 220 bytes ~ 1 million bytes

1 GB = 1024 MB = 230 bytes ~ 1 billion bytes

Quiz

Q1: 64MB = ? Bytes

Q2: 2GB = ? Bits

Classification of Memory

Main Memory

Backing Storage Devices

Cache Memory

How Main Memory works with CPU ?

00000001

0010 READ A0011 READ B

0100

00100010

READ A

READ A

+1MAR

MDR

控制部件

地址譯碼器

指令譯碼器

主要記憶體

Main Memory

RAM: Random Access Memory

ROM: Read Only Memory

ROM (top) and RAM (bottom) on a motherboard (right)

RAM

1.Data can be read from any word or written onto any word in the RAM.

2.When a program is run,the instructions and the working data are temporarily stored in the RAM.

3.When the computer is switched off,all the data held in the RAM are lost.RAM is therefore volatile.

Different types of RAM

There are two basic types of RAM,

dynamic RAM and static RAM.

DRAM

DRAM (Dynamic RAM) is a type of

memory that must be re-energized

constantly or its contents will be lost.

1.SDRAM (Synchronous DRAM) is a faster

version of DRAM because

it is synchronized to the system clock.

2.RDRAM (Rambus DRAM) is a newer

type of DRAM that is even faster than

SDRAM.

SRAM

SRAM (Static RAM) is faster and more

reliable than any form of DRAM,

but are more expensive.

SRAM does not have to be re-energized as

often as DRAM.

Comparison between DRAM and SRAM

– Like a rechargeable battery

– Every read, discharging the battery, need to recharge.

– Even you do not read, it will discharge!

– Need to recharge periodically.

– Slow.– Use in

motherboard

– Like a light bulb– No discharging– Relatively Fast– Use in CPU, as

register

DRAM SRAM

ROM

1.Data can only be read from the ROM.The contents cannot be overwritten.

2.ROM is used by the computer manufacturer to store the systems programs.These programs control the fundamental operations.

3.ROM is non-volatile.When the power is switched off,the contents of the ROM remain unaffected.

Different types of ROM

1. A programmable read-only memory (PROM)

2. Flash memory or Flash ROM

Summary on different types of computer memory

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