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
$300
2)Small storage with high speed
$500
3)Large storage with high speed
$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 ?
控制部件
+1
MAR
主要記憶體
0010
0010
地址譯碼器
READ A
指令譯碼器
MDR
READ A
0000
0001
0010 READ A
0011 READ B
0100
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
DRAM
– 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
SRAM
–
–
–
–
Like a light bulb
No discharging
Relatively Fast
Use in CPU, as
register
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
~ The End ~