From: doug@cs.dartmouth.edu (Doug McIlroy)
Subject: [TUHS] [TUHS} PDP-11, Unix, octal?
Date: Mon, 16 Jan 2017 21:23:07 -0500 [thread overview]
Message-ID: <201701170223.v0H2N7Q9010667@coolidge.cs.Dartmouth.EDU> (raw)
> I understand why other DEC architectures (e.g. PDP-7) were octal: 18b is
a multiple of 3. But PDP-11 is 16b, multiple of 4.
Octal predates the 6-bit byte. Dumps on Whirwind II, a 16-bit machine,
were issued in octal. And to help with arithmetic, the computer lab
had an octal Friden (IIRC) desk calculator. One important feature of
octal is you don't have to learn new numerals and their addition
and multiplication tables, 2.5x the size of decimal tables.
Established early, octal was reinforced by a decade of 6-bit bytes.
Perhaps the real question is why did IBM break so completely to hex
for the 360? (Absent actual knowledge, I'd hazard a guess that it
was eased in on the 7030.)
Doug> I understand why other DEC architectures (e.g. PDP-7) were octal: 18b is
a multiple of 3. But PDP-11 is 16b, multiple of 4.
Octal predates the 6-bit byte. Dumps on Whirwind II, a 16-bit machine,
were issued in octal. And to help with arithmetic, the computer lab
had an octal Friden (IIRC) desk calculator. One important feature of
octal is you don't have to learn new numerals and their addition
and multiplication tables, 2.5x the size of decimal tables.
Established early, octal was reinforced by a decade of 6-bit bytes.
Perhaps the real question is why did IBM break so completely to hex
for the 360? (Absent actual knowledge, I'd hazard a guess that it
was eased in on the 7030.)
Doug
=
next reply other threads:[~2017-01-17 2:23 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-17 2:23 Doug McIlroy [this message]
2017-01-18 16:47 ` Clem Cole
2017-01-18 2:33 Noel Chiappa
2017-01-18 3:06 ` Steve Johnson
2017-01-18 3:36 ` Dan Cross
2017-01-18 6:53 ` Angelo Papenhoff
2017-01-18 7:31 ` ron minnich
2017-01-18 8:09 ` Angelo Papenhoff
2017-01-18 21:04 ` Steve Johnson
2017-01-18 21:42 ` Charles Anthony
2017-01-18 6:04 ` Lars Brinkhoff
2017-01-18 18:47 ` Peter Jeremy
2017-01-18 18:58 ` Charles Anthony
2017-01-18 14:28 Nelson H. F. Beebe
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