HP 19C versus HP 95C

[Dieter]

(04-22-2018 04:08 PM)Cosmo Wrote:  The ratio steps/registers seems not very well balanced. Which program requires so may registers and 98 steps ?

I agree that there are not many programs that fit in 98 steps and require as much as 30 data registers. For instance I remember a 19C/29C program that solves linear equation systems with 6 unknowns (here only a triangular matrix is stored). A classic application for programmable calculators of this kind was solving a 4x4 system, which – assuming the complete matrix is stored – requires 20 registers plus a few for the program itself.

Assuming the usual 7:1 steps-per-register ratio the 19C and 29C have a total user memory of 98 + 7*30 = 308 bytes (plus stack, plus mode settings etc.). If this had been equally used for data and program this would have been 154 steps and 22 data registers. Or maybe 168 + 20. Which sounds more reasonable, or at least more practical for most applications.

But this includes the volatile memory part. If the technical limitations in 1977 did not allow for more than 98 + 7*16 = 210 bytes of continuous memory this means that it has been almost equally distributed between data and program (112 + 98).

(04-22-2018 04:08 PM)Cosmo Wrote:  In my opinion it would have been fine to convert the extra 14 registers (despite volatile) into extra programming steps.

Here I do not agree. IMHO using the volatile part for programs is not an option – turn off the calculator and lose a part of your program, so that probably the remaining part will no longer work as well. Considering only the continuos part, maybe 10 registers + 140 steps would have been possible. But in this case others may have felt that merely 10 "continuous" data registers is less than what they expected.

It didn't take long after the appearance of the 19C and 29C when the first HPs with reallocatable memory showed up. This way you could choose between more data or longer programs. There are cases for both scenarios, so this maybe is the best solution.

Dieter