HP-34C Single Use I Register

[Gene]

Correct. Not at the same time.

Same as for the HP-67/97's I register. If you are using it for looping, you can't use it for something else unless the value used in looping is used to address memories or such. To load memories 1 - 9 the I register could be used to loop and store the value indirectly.

Any machine with a single I register would face the same chokepoint at the single I register - you can't loop from 1 to 9 and also be storing the values into the odd registers without manipulating the value in I since there is only the one register.

The HP-41 of course could use any register, but not the 67/97, 34C, 29C, etc.