Normally, we talk about the CPU, will say the program is a 32-bit compiler, you can run in 32-bit or 64-bit machine machine, or it is when you download some open source packages, it can be divided into 32-bit CPU version or 64CPU-bit version, or when looking at the composition of computer-related books, especially when it comes to X86 CPU, will certainly 8086/80286/80386 out for the thing, and it will mention 8086/80286 is a 16-bit CPU, 386 from the beginning of a 32-bit CPU , 16/32/64 bit of what this says is that the CPU index? In fact, here to talk about is the CPU word length.
First, the computer's "word"
In the computer, a series of binary digital processing or as a whole operation, referred to as a computer word, referred to as words. Word is usually divided into several bytes. In a memory, each cell typically stores one word, each word is addressable. Represented by the word length bits. In the arithmetic unit CPU, a controller, typically in word units are transmitted. Words appear in different address its meaning is not the same. For example, the word is sent to the controller command, and sent to the operator is a number to a word.
Second, the word length
Digit word length is the particular CPU can handle at one time, also the length, i.e. the number of bits a CPU capable of parallel processing.
Have a great relationship with the word computer functions and purposes, it is an important technical specifications of the computer. A word length directly reflects the accuracy of the computer, to meet the cost of the relationship between the different requirements and operational coordination and precision hardware, most computer support variable length operation that can be achieved within a half-word machine, the entire word (or word length) and dword operations. Other indicators are the same, the greater data processing speed faster computer word length. A 16-bit word of a PC, can be processed directly within the digital power 16 (65536) 2, the method requires more than 65,536 digital decomposed to handle. 32 pc-16 than the superior reason is that the digital machine in one operation it can handle the large, 32-bit digital word length PC can directly address up to (2 to the power 32) 4000000000, processing can the higher the number, the fewer the number of operations, so that the higher the efficiency of the system. Early computer word length is usually 8 and 16, most of the 386 and 32-bit or higher processor. At present most of the computer's processor market has reached 64.
Three, CPU word length determined by what
CPU word size is determined by the CPU chip data bus width. There are internal CPU and the external data lines of the data lines, such as the 8088 CPU internal data line 16, and the 8-bit external data lines, then it is said word length is 16 bits, 16-bit processors is still only but yes transmission data in 8-bit mode to exchange data when the CPU and memory. Another example Pentium4 the CPU internal data line 32, and the external address lines are 36, 64-bit external data lines, it is still 32-bit word length, so Pentium4 or 32-bit processor, the processing can not be called 64 device.