My current computer (intel dual core 6700 at 2,66 GHz) is equiped with
Vista Ultimate and I am unable to run UBASIC on it. UBASIC is an old MSDOS application and its main advantage is that it has long precision maths tools (2600 digits) and therefore much used by number theorists
and, in general, users who like to do some recreational math.

My old system had 'command.com' available, but no more so in Vista
it seems. I can only find and run 'cmd.exe' but that gives a compatibility
error message.

So I installed your MSDOS emulator DOSBox ver 0.70.
After changing the keyboardlayout and learn how to'mount' etc.
I was able to get UBASIC up and running!

First question. Did I made the right choice for running UBASIC
in this DOSBox emulator shell ?

My main interest is to get the highest possible speed. The default
value of 3000 Cpu Cycles looks quite sluggish.
A short dummy benchmark program in UBASIC like

100 clr time
200 A=0
300 for I=1 to 1000000
400 A+=1
500 next I
600 print A
700 print time

gives with default Cpu Cycles of 'auto' (3000) a timing of 0:01:31
and is almost equal to real world timing.

Raising Cpu Cycles to 150000 gives an astonishing 0:00:01
But with the above 150000 cycles my stopwatch says it took around
6 seconds instead of 1 second on display. Yet 6 seconds is still
a formidable improvement compared to the one minute and a half
from the 'auto' mode.

Overdriving to a million will let disappear the blinking
of the prompt cursor and the program environment seems
to come to a halt. No gain in speed is obtained while
running the program.

What advice can you give me regarding the setting of the
Cpu Cycles in combination with running UBASIC as fast as
possible ?