Speed of the HP-41CL

[MichaelG]

I recently watched a video on YouTube that shows a speed comparison of the 41CL and 41CX. My feeling was that the CL was about 4 time faster (or a bit more). The maximum turbo mode of the CL is 50.

Where does this big difference come from? I know the example makes intensive use of X-Memory. Does this slow down everything? Run "normal" focal programs faster?

Michael

[Eric Smith]

In the 50x turbo mode, many, but not all, of the 41's microinstructions run at 50 times the normal speed. However, certain microinstructions, including all the ones that access the display and peripherals, have to run at normal speed, so those run at 1x, or perhaps even slower due to the delay to sync up to the 1x serial bus. This results in the average execution speed being much lower than 50x. The actual speed will vary a lot depending on exactly what your program is doing.

Edited: 17 Jan 2012, 3:56 a.m.

[BobVA]

I don't think it's the X-MEMORY access, but rather what Eric mentioned above, the need to stay in sync with hardware not on the CPU board. In particular the 41CL manual notes that the keyboard must be scanned (a 1x operation) at every program line, which limits the speedup a program composed of relatively simple functions would see.

For example, a program that made multiple calls to transcendental functions would see a lot bigger speed boost than one that was just incrementing a counter.
Cheers,
Bob