🚀 go-pugleaf

>Speaking of the 1130/1800, does anyone know of any other architectures
>that are binarily compatible but use different "word" sizes?  If I
>remember correctly, the 1130 used 16-bits while the 1800 used 18-bits(?).

The 1130 had, as I remember, 16 bits per word plus two parity bits. 
(I'm certain about the 16 bits per word.)  As I remember, the 1800 had
16 bits per word plus one parity bit plus a "write protect" bit, which
could be set (or maybe cleared, it may have been a "write enable" bit)
to prevent attempts to write to a location.

The registers were 16 bits long on both machines, the instructions were
16 or 32 bits long, and all data items were 16 bits long or a multiple
thereof.  I.e. you had 16 data bits per word on both architectures;
MAXINT was 32767 on both machines.

>But they both used the same instruction set and software.

Well, not exactly; the 1800 had some additional instructions and ran a
different OS.