How the word-length of an ISA is implemented in the hardware and software?

Question

I have learnt that word-length is an ISA feature, which has to be implemented in hardware and software both. I have a vague idea only about the answer. I need correction or confirmation. Does the word-length becomes size of the general purpose register in the CPU? Does the word-length become the size of the 'int'(just plain int, not long or short) for a compiler?

score 2 · Answer 1 · answered Feb 27 '11 at 17:26

The word length is the number of bits natively handled by the system. Common versions right now are 32-bit words and 64-bit words.

For example, a byte can hold a number from 0-255. However, a 32-bit integer is from 0-4,294,967,295. An integer is the native "word size" of the system, so is 4-bytes wide in 32-bit systems and therefore is considerably larger than 0-255.

In fact, in many systems/compilers/etc. types which are smaller than a system's native word size are converted to that word size simply because it's more efficient than trying to put multiple values into a single word. A boolean, for example, can be represented by a single bit. However, if you write a piece of software that uses 32 boolean values, it's not going to squeeze them all into a single word. Each will be assigned its own word when it runs on the metal.

@Neera I have revised the question to become more clear on what information I am seeking. kindly find sometime to read it again and answer. — KawaiKx, Feb 28 '11 at 01:56

score 1 · Answer 2 · edited May 23 '17 at 12:11

1

I am taking liberty and interpreting this question as size of integer on a computer in C or C++. In that case this link will help - Does the size of an int depend on the compiler and/or processor?. However if read it literally then size of word of CPU should be size of its register.

edited May 23 '17 at 12:11

Community

1
1

answered Feb 27 '11 at 17:34

Neera

1,577
8
10

score 0 · Accepted Answer · answered Mar 01 '11 at 01:31

Hardware implementation : Word-length is the number of bytes fetched by the CPU at a time and can also be called the natural size of the machine. though there is nothing natural about the computers. it also becomes size of the CPU's register in implementation, since it needs registers to store what it fetches. Having said that, it is possible to use a bigger register for storing purpose. IA-32 softwares (with word length 32bits) can run on x86-64 (with word length 64 bits). Software implementation: word-length becomes the size of 'int' (just plain int, not long,short)

How the word-length of an ISA is implemented in the hardware and software?

3 Answers3