Speed on the 41 family


Hi all…

I was playing with a 41C, CV and CX, and wrote a trivial program to test the speed of the machines.

LBL 01
GTO 01

The 41C finished in 1min 31secs.
The 41CV finished in 1min 36secs.
The 41CX finished in 1min 33secs.

Does anyone know if this is the correct behavior? Is the 41C the fastest machine?

I used the same battery pack on all machines, so battery charge should not be a factor.
I don’t know if it is relevant, but the serial numbers are:
41C - 2241B10840
41CV – 2552S21053
41CX – 2819S21707

Any ideas?

Also, I would like to publicly thank Luiz Vieira for resurrecting my old 41C.
I really appreciate that my friend!



Hey, Silvio; my pleasure!

Thank you for the kind acknowledge. This is gold... I must confess that when I saw your post, my first intent was to ask if you and your wife had a nice trip back to USA and about that babe; good news, indeed!

Just a question: are all of these 41 the same type? Full or half nut? I know that the 41C you sent me is a fullnut type, but the others share the same architecture?

Also, if you run a program the first time and it has GTO or XEQ to "short-" or "long'-"term LBL (2 or three bytes), it's gonna be a lot slower than the next executions because the 41's O.S. will compute the number of bytes necessary to "jump", forward or backwards, in the first GTO/XEB occurrence. This does not happen with XEQ"ROMfunction". And if you pack the calculator memory, all the process is repeated.

I have not felt significant difference from any of the HP's (C/CV/CX), but I guess the CX MAY (just a guess) be slower because of the internal circuitry. Also we must consider that the HP41CV has more memory space and more circuitry than the 41C. But based in your measurements, the 41CV is even slower than the 41CX.

The last argue: what modules were installed in the calculators, if any?

I have some knowledge about HW, and loosing clock cycles is a potential cause of crash in clock dependant devices, mostly earlier architectures, and this fact leads me to believe the only reason for the difference is an acceptable "range" (2 to 5%) in component values, causing a slightly different clock for each machine. You may measure two 41C's running time and find different values.

A few weeks ago my HP41CX scared me a lot, but I believe it's just a matter of failure in the batteries' contacts. I believe that sort of "bad behavior" will only be observed in an HP41CX or an HP41 with a time module.

BTW, would you help me finding an HP41CX, fullnut type? If you believe you can, please, e-mail me.

Grande abraço! (let's say it's a version of a closer "Cheers!")

Luiz C. Vieira


Luiz is right that the execution speed is varying according to installed ROM modules and compiling GOTOs etc. But most likely you get variations because the clock circuitry is using an L-C oscillator rather than a precise quartz. And those L-C components have large tolerances.


Hi Silvio,

Luiz is right as he states the component's tolerances as the responsible factor for the deviation of between 5% to 6%. AFAIK the inductor has a tolerance of 10%. So,the deviation is fully OK.
Regards, Andreas


I remember some guys in the University that changed the resistor to get the HP-41C/V/X run faster.



Actually they lowered the capacitance of the L-C oscillator. One could also change the inductance but those aren't easy to find. If you like it switchable you can solder in a smaller C and another one switched in parallel to get the original C value. Cparallel = C1 + C2. As switches you may choose a microdip (needs mech works on the case) or a reed relais (operated with an little external magnet / keep away from magnetic cards!).

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