| Re: C64 compared to the Plus 4? [message #4969 is a reply to message #4939] |
Wed, 02 May 2012 00:10   |
Anton Treuenfels
Messages: 105
Registered: December 2011
Karma:
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Senior Member |
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From Newsgroup: comp.sys.cbm
"dott.Piergiorgio" wrote in message
news:Slenr.163886$GZ3.42029@tornado.fastwebnet.it...
> Il 29/04/2012 13:03, Christian Brandt ha scritto:
>> Am 25.04.2012 15:09, schrieb MagerValp:
>>
>>> It's about 12% slower while graphics is displayed, but 78% faster when
>>> it's not (in the borders). I don't have the details here, but iirc it
>>> works out to a PAL Plus/4 having about 40% more CPU cycles than a C64.
>>
>> The C64 CPU also does waitstates while the VIC reads graphic data from
>> memory. I remember you lose up to 66% of all memory cycles upon every
>> eigth line displaying data.
>>
>> All in all the 265/Plus4 is a lot faster than the C64 and sometimes
>> even faster than a C128 running at 2Mhz (I think this may come from the
>> slow MMU-Handling of the C128).
>
> IIRC, in an Compute! book (on C-128 ?) the speed issues was also
> attributed to the BASIC parsing, the gist of it being that the token
> scanning loop takes more time to look up into the larger basic 3.5, 4.0
> and 7.0 token list, I don't know if is true (and that I remember well),
> but at least makes sense.
>
> Opinion on this ?
That doesn't make any sense at all. Scanning the larger token tables matters
only during tokenization (entering program lines), not during execution
(running programs).
However C128 BASIC takes a lot longer to fetch anything at all from RAM than
the C64 or VIC20 because the BASIC ROM is in a different memory space. Every
byte fetch of program text or variable memory has to go through two bank
switches, from the BASIC ROM space and back again. Also the main BASIC
control loop is longer, so statement-to-statement time is a little slower
The BASIC ROMs of the C64 and VIC20 are in the same memory space as program
text and variable memory, so they don't bank switch at all. OTOH, they have
a lot less RAM space than the C128 for BASIC programs. Their main control
loops also don't try to do as much as the C128's.
The 2MHz mode of the C128 covers up a lot of the slowdowns, too.
- Anton Treuenfels
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