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Group count - word length

2020-11-06 01:16:16 Qishan

Machine word length :CPU The number of bits of data that can be processed at one time , Usually with CPU The number of registers is related to .
Storage word length : A storage unit in memory ( Storage address ) The number of bits of binary code stored , In memory MDR Number of digits .
Instruction word length : The number of digits in a computer instruction word .
Data word length : The number of bits occupied by computer data storage .

notes : In von Neumann , Instructions and data are equally important , It's all stored in memory , And you can search by address .

Usually early computers : Storage word length = Instruction word length = Data word length . Therefore, one access can take one instruction or one data , With the continuous expansion of the scope of computer application , The three may be different , But they have to be integral multiples of bytes .

The unit of information storage in a computer

Information in a computer is represented in binary , Common units are position 、 Bytes and words .

1、 position (bit): It's the smallest unit of data in a computer ( Storage element ), A binary number holds one bit , namely 0 or 1. It is also the smallest unit of information in memory , Usually use “b” To express .

2、 byte (Byte): Byte is the most commonly used basic unit of storage capacity in a computer ( Storage unit ). One byte by 8 Bit binary number composition , Usually use “B” Express . A character takes up a byte , A Chinese character takes up two bytes . Other common storage units are :

Storage capacity is measured in bytes B、 kilobytes KB、 Megabytes MB And billions of bytes GB etc. . The conversion relationship between them is as follows :

1KB (Kilobyte kilobytes )=1024B
1MB (Megabyte Megabytes abbreviation “ mega ”)=1024KB
1GB (Gigabyte Gigabyte also called “ Gigabit ”)=1024MB
1TB (Trillionbyte Trillion bytes Terabytes )=1024GB
1PB(Petabyte Billions of bytes Petabyte )=1024TB
1EB(Exabyte 10 billion bytes Ebyte )=1024PB
1ZB (Zettabyte One trillion bytes Zebyte )= 1024 EB
1YB (Jottabyte 100 billion bytes Yao byte )= 1024 ZB
1BB (Brontobyte 100 billion bytes )= 1024 YB

3、 word (Word) And word length : Word refers to being accessed as a whole in a computer 、 delivery 、 To deal with the A set of binary numbers . One word digit ( That is word length ) Is an important feature of computer system architecture . The word length is determined by CPU The type of , Different computer systems have different word lengths , Common are 8 position 、16 position 、32 position 、64 I'm waiting for you , The longer the word is , The more bits of information a computer processes at a time , The higher the accuracy , Word length is an important indicator of computer performance , At present, mainstream microcomputers are being developed by 32 Bit machine to 64 Bit machine transition .

 ** Pay attention to the difference between word length and word length , Words are units , And word length is the indicator .**

The word length of the machine will affect the speed of the machine . if CPU The word length is shorter , We have to calculate more bits of data , It takes two or more operations to complete , This is bound to affect the running speed of the whole machine .

The word length of the machine also has a great impact on the cost of hardware . It will directly affect adders ( or ALU), The data bus and the number of bits of memory word length . Therefore, the machine word length can not be considered only from the accuracy and the range of number representation .

In order to adapt to different requirements and coordinate the relationship between calculation accuracy and hardware cost , Most computers support variable word length operations , In other words, half word length can be realized in the machine 、 It's full length ( Or single word length ) And double word length operations .

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