a byte

A byte is a group of 8 bits handled together as one little package. Bits are too tiny to be a convenient unit on their own, so computers bundle them into bytes the way a shop sells eggs by the dozen rather than one at a time. A byte is the smallest chunk of memory most machines give a unique address to, so it is the natural grain at which data is stored and moved.

Because a byte is 8 bits, it has 2^8 = 256 possible patterns, which can represent the whole numbers 0 through 255, or a single English character, or one of 256 shades. People often write a byte in hexadecimal as two hex digits (each hex digit standing for exactly 4 bits), so the byte 0b11001010 is written 0xCA. File sizes build up from here: a kilobyte is about a thousand bytes, a megabyte about a million, a gigabyte about a billion (storage makers usually mean exact powers of ten, while operating systems often count in powers of two, 1024 bytes to a kibibyte, which is why a '1 TB' drive shows as a bit less).

Watch the capital letters: a byte is written with a capital B and a bit with a lowercase b, and they differ by a factor of eight. The 8-bits-per-byte convention is now universal, but it was not always — some early machines used 6, 7, or 9 bits, which is why strict standards documents prefer the unambiguous word 'octet' for exactly 8 bits.