Byte sizes (was Re: 2.8M 3.5' floppy

[Tony Duell]

> 
> > Umm 6 bits is perfect for BCD, look at IBM's 1620 : 4 bits BCD, 1 bit 
> > sign flag/length flag 1 bit parity
> 
> Very inefficient. I hope you are not serious.

I don;t know much about IBM stuff, but I do know that the HP9100 
calculator had 6-bit memory locations (this is obvious from the 
schematics of the memory data board, from the fact that the main CPU 
register (register '2', for some odd reason) is 6 bits wide, etc.

These were used in 2 ways. Either to store a user keycode (there were 64 
keys [1]), or to store a BCD digit. I seem ro rememebr in the latter 
case, the 2 extra bits were a sign bit and a blanking flag.

[1] yes, I know the 9100B has 65 keys. 2 of them are wired electrically 
in parallel and send the same code. One is 'hyper', the other is one of 
the memory transfer functions. If that keyvcode is followed by a trig 
function, it's taken as 'hyper'., if it's followed by an address, it's 
the memroy function.

-tony