Word

In the widest sense, a word is an ordered group of bits considered together. In computer architecture, a word may denote data processed by the CPU, an instruction, an address, or the unit by which main memory is accessed. In early and simple computers, these were to a large extend the same width. However, contemporary practice is to give each byte in main memory its own address; instructions are often smaller than the ALU width; virtual and physical addresses are different size, etc.

Words are now usually a power-of-two multiple of an 8-bit byte in size, but in early computers, other word sizes were common. 36 bits was a very popular size on early mainframes, such as the IBM 704 and its descendants, the Honeywell 6000 series‎‎, and the PDP-10 family. However, small word sizes were common too, e.g. the 12-bit words of the PDP-8 family.