The Evolution of Byte Sizes

Byte has to be one of the most recognizable parts of the digital lexicon. It's an incantation that can be recognized by even the uninitiated. But where does the byte come from? Has it always existed, or did it more recently come into being? And, more specifically, why is a byte 8 bits? Is it some holdover from long ago, or is there some iron clad rule of 8's?   Selected Sources:   https://archive.org/details/byte-magazine-1977-02/page/n145/mode/1up?view=theater - Buchholz on the "byte" in BYTE!   https://sci-hub.se/10.1049/pi-3.1949.0018 - A STORAGE SYSTEM FOR USE WITH BINARY-DIGITAL COMPUTING MACHINES   https://ia600208.us.archive.org/32/items/firstdraftofrepo00vonn/firstdraftofrepo00vonn.pdf - The First Draft of a Report on EDVAC