18 Jan
2017
18 Jan
'17
12:04 p.m.
Steve Johnson wrote:
Historical note: before networking, magnetic tapes
were essential for
backups and moving large quantities of data. Data was stored in
magnetic dots running across the tape, and typically held a character
plus a parity bit. Thus, there were 7-track drives for 6-bit machines,
and 9-track drives for 8-bit machines. But nothing for 9-bit
machines...
The 36-bit PDP-10 initially used 7-track drives, with six frames to a
word. During its lifetime sunset, 7-track drives were no longer made,
so 9-track drives were used instead. The most common encoding was to
store a word in five 8-bit frames, with four bits unused.
The PDP-10 did not have a fixed byte size. Were there any 9-bit
machines?