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:
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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 ? 控制部件 +1 MAR 主要記憶體 0010 0010 0000 0001 0010 READ A 0011 READ B 0100 地址譯碼器 READ A 指令譯碼器 MDR READ A
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.
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 Comparison between DRAM and SRAM 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