From mboxrd@z Thu Jan  1 00:00:00 1970
From: lars@nocrew.org (Lars Brinkhoff)
Date: Wed, 18 Jan 2017 07:04:31 +0100
Subject: [TUHS] [TUHS}  PDP-11, Unix, octal?
In-Reply-To: <50a7fbcbb6af280eb108fff1361c37ee1718bff0@webmail.yaccman.com>
 (Steve Johnson's message of "Tue, 17 Jan 2017 19:06:28 -0800")
References: <50a7fbcbb6af280eb108fff1361c37ee1718bff0@webmail.yaccman.com>
Message-ID: <86lgu8rjio.fsf@molnjunk.nocrew.org>

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?