FTGH clear-out at Mesa Electronics, Richmond, CA, USA
paulkoning at comcast.net
Thu May 25 10:13:36 CDT 2017
> On May 25, 2017, at 10:41 AM, Noel Chiappa via cctalk <cctalk at classiccmp.org> wrote:
>> From: Anders Nelson
>> Heavens, why are the bit positions in descending order right to left in
>> that PCM-12?
> Numbering bits in descending order from right to left (AKA increasing order
> from left to right) used to be the standard - IBM S/360, PDP-10, etc, etc
> all did it that way.
For some definition of "standard". It seems that IBM did this, and DEC prior to the PDP-11, but other machines of that time or earlier numbered bits according to the power of 2 they represent, i.e., the "current standard". CDC and Burroughs are examples.
I just went back a bit, and found something interesting: the Dutch machine ARRA (around 1951, relay based, only worked once) has IBM style bit numbering. But its successor ARRA II (1953, tubes) uses "current" ordering. Perhaps the reason is that the description of ARRA II was written by Dijkstra.
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