Gregory's Server@kenshirriff This thread is very interesting! Thanks for the breakdown. I'm curious what it means for a computer to be 24-bit but operate with a 1-bit ALU and 1-bit I/O. What part is 24-bit?
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3 comments
 @tanavit @kenshirriff So if a "register" contained 2**24-1 (all 1s) and then the program added 1 (overflowing), the register would see 24 different states (1 for each bit), and after the first cycle it would have appeared to have subtracted 1 bit, first setting the lowest bit to 0 while the remaining 23 bits were still set to 1. Do I have that right? If that is the case, was the program written to include some check-pointing logic to avoid reading interstitial states after a power loss?  @dvogel You can think of it as a 24-bit architecture with a 1-bit implementation. Similar to the PDP-8/S, which implemented the 12-bit PDP-8 architecture with serial circuitry. Also, the Datapoint 2200, a serial 8-bit computer whose architecture was copied to create the Intel 8008 chip. (That's why x86 is little-endian; you have to start with the lowest bit on a serial machine.) |
@dvogel @kenshirriff
A word is 24 bit, but arithmetic operations are made one bit by one bit, beginning by least significant one.
We do the same in 10 base. first adding the units then the tens then the hundreds...