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 .