Re: Overclocking an Apple ][?

[mjmahon@aol.com (Michael J. Mahon)]

Simon replied:

>Michael J. Mahon <mjmahon@aol.com> wrote:
>
>> Simon Williams wrote:
>> 
>> >Michael J. Mahon <mjmahon@aol.com> wrote:
>> >
>> >> The Apple IIc+ is such a two-domain system, and it alone
>> >> offers the possibility of easy overclocking of its "fast"
>> >> processor/cache domain.
>> >
>> >Which brings us back to the original question of what might be wrong
>> >with _my_ IIc+... since it seems to function perfectly well aside from
>> >the aforementioned lack of speed.
>> 
>> Hi, Simon!
>> 
>> This problem is sufficiently exotic that it makes me wonder
>> exactly how you know what speed your machine is running
>> at.
>
>The short answer is "I don't"  
>It seems my method of drag racing the IIc+ against other Apples was a
>bit misguided. I had them doing:
>
>10 FOR I = 1 TO 10000 : PRINT I : NEXT
>
>With the result being that the IIc+ was running slightly slower than a
>stock IIe. 
>
>> As you probably know, the IIc+ is a Zip Chip "workalike", and
>> it can be configured to run at various speeds and to slow down
>> for certain slots, speaker, joystick, etc. by a configuration
>> utility that usually runs just after ProDOS loads.
>
>Which made me wonder about the validity of my test, so I changed it to:
>
>10 FOR I = 1 TO 10000 : NEXT
>20 PRINT CHR$(7)
>
>Without printing to the screen, the IIc+ ran the test considerably
>faster than my IIgs (in fast mode), so I can only conclude that a) I've
>spent several days worrying about nothing and b) the IIc+ slows down
>dramatically when printing text. 

The reason is that your test spends the vast majority of its time
scrolling the display, and all writes to memory run at 1MHz.

The empty FOR loop is a better test, since it runs a lot of
code from ROM and only updates a few interpreter variables.

In general, the part of a program that changes the screen will
run unaccelerated, while the part that simply computes with
relatively few stores will experience maximum acceleration.

If you were taking the square root of I and then printing,
you would notice the difference even with the scrolling
overhead.

Glad your IIc+ is healthy!  ;-)

-michael

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