Re: 'Frankenstein' Disk Drives, Done Cheap

From: Nate Lawson <>
Date: Sun, 4 May 2014 16:04:54 -0700
Message-Id: <>
On Apr 25, 2014, at 7:35 PM, Pete Rittwage <> wrote:

> On Fri, April 25, 2014 10:25 pm, Jim Brain wrote:
>> On 4/25/2014 1:22 PM, Ingo Korb wrote:
>>> "smf" <> writes:
>>>> I guess commodore dropped the ball again as the 1571 connected to a
>>>> zoomfloppy can run really fast.
>>> As far as I can tell from occasional postings on various forums, the
>>> Zoomfloppy/1571 combination seems to suffer from reliability problems
>>> and the usual advice given is to use a very short, high quality
>>> cable. Therefore it appears that Commodore did not "drop the ball again"
>>> but instead chose reliability over speed, which most sane companies
>>> would do in this situation to reduce support costs and to avoid the
>>> impression that their products are unreliable.
>>> -ik
>>>        Message was sent through the cbm-hackers mailing list
>> We probably (if it's not an option already) should have an option for
>> slowing down the SRQ transfer bit rate to create a "known good" transfer
>> speed with flags to speed it up if it works.
> Arnd Menge wrote that code, but as I recall, it has to get a byte on or
> off the disk in less than 32 cpu cycles (possibly ~64 in 2MHz mode), so I
> believe it was tuned how it needed to be to replace the parallel cable.  I
> doubt it could be slowed down…

As I mentioned in my presentation, you have a max of 25 microseconds per byte. At full speed, the CIA takes 16 microseconds per byte. The next slower speed would be 32 microseconds/byte, which is too slow to keep up with a 300 RPM drive.

You could use a slower speed for a regular accelerator, but it would not be useful for what I was targeting, which was streaming reads of an entire track at once in order to read all copy protected bits.


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Received on 2014-05-04 23:07:13

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