What is a 32 bit or 64 bit computer? What is Word Size in Computers?

3 definitions from 3 different sources!

Head First C

What do 8-bit and 64-bit actually mean?

Technically, the bit size of a computer can refer to several things, such as the size of its CPU instructions or the amount of data the CPU can read from memory. The bit size is really the favored size of numbers that the computer can deal with.

Principles of Computer Organization and Assembly Language - Using the Java Virtual Machine

The definition and size of a word are not absolute, but vary from computer to computer. A word is the size of the most convenient block of data for the computer to deal with.

For example, the Zilog Z-80 microprocessor had a word size of 8 bits, or 1 byte. The CPU, memory storage, and buses had all been optimized to handle 8 bits at a time (for example, there were eight data wires in the system bus). In the event that the computer had to process 16 bits of data, it would be handled in two separate halves, while if the computer had only 4 bits of data to process, the CPU would work as though it had 8 bits of data, then throw away the extra 4 (useless) bits.

Formally speaking, the word size of a machine is defined as the size (in bits) of the machine’s registers. A register is the memory location inside the CPU where the actual computations, such as addition, subtraction, and comparisons, take place.

The Intel 8088, for example, had four 16-bit general-purpose registers, while the Intel 80386, designed seven years later, used 32-bit registers instead.

Computer Systems - A Programmers Perspective

Running throughout the system is a collection of electrical conduits called buses that carry bytes of information back and forth between the components. Buses are typically designed to transfer fixed-sized chunks of bytes known as words. The number of bytes in a word (the word size) is a fundamental system parameter that varies across systems. Most machines today have word sizes of either 4 bytes (32 bits) or 8 bytes (64 bits).