Why are typical UART baud rates not in multiples of 1000?

Question

Why are typical baud rates not in multiples of 1000 instead of being in multiples of 300 i.e. 4800, 9600, 19200, 115200, etc...? Is there a mathematical or electrical reason behind this?

Answer 1

This goes way, way back to the Bell 103 modem from 1962. It operated at 300 bits per second for reasons deriving from the use of audio frequency-shift keying to modulate data; the frequencies available were limited by the quality of the phone lines. All common serial data rates since then are integer multiples of this rate.