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From: Lars Brinkhoff <lars@nocrew.org>
To: John Cowan <cowan@ccil.org>
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 (John Cowan's message of "Wed, 3 Feb 2021 15:07:46 -0500")
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Subject: Re: [TUHS] 2^n-bit operands (Was reviving a bit of WWB)
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John Cowan wrote:
> On the 36-bit PDP-10, things were better: the sign bit was mostly ignored
> and five 7-bit ASCII characters were packed into each word, again with NUL
> padding.  (Line editors turned on the sign bit to indicate that this word
> held an explicit ASCII line number.)

It was not the sign bit but the least significant bit.  The ILDB/IDPB
byte instructions prefer it that way.