The Art of Assembly Language, 2nd Edition

2.3 Data Organization

In pure mathematics a value's representation may take require an arbitrary number of bits. Computers, on the other hand, generally work with some specific number of bits. Common collections are single bits, groups of 4 bits (called nibbles), groups of 8 bits (bytes), groups of 16 bits (words), groups of 32 bits (double words or dwords), groups of 64 bits (quad words or qwords), groups of 128 bits (long words or lwords), and more. The sizes are not arbitrary. There is a good reason for these particular values. This section will describe the bit groups commonly used on the Intel 80x86 chips.

2.3.1 Bits

The smallest unit of data on a binary computer is a single bit. With a single bit, you can represent any two distinct items. ...