Stephen Satchell list at
Fri Feb 22 19:47:40 UTC 2019

On 2/22/19 11:27 AM, bzs at wrote:
> I don't know the high-water mark for the number of IMPs or more
> specifically how many existed on the NCP->TCP flag day but I'm pretty
> sure the theoretical maximum was 256 tho no doubt someone had a way to
> extend that. But, w/o extensive changes, 256, probably 254, not sure 0
> or 255 could be an IMP number, whatever!

There was no node 0 or 255.  So the number of nodes was capped at 254.
For each node, there were subnodes so that multiple computers at each
location could be addressed.  It wasn't a full 8-bit field.

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