[Coco] 5 1/4" drive

[Gene Heskett]

On Tuesday 07 April 2009, Christian Lesage wrote:
>Gene Heskett wrote:
>>> Only if you can set it to rotate at 300 RPM. Normally, those 1.2MB 5.25"
>>> drives spin at 360 RPM and have a 300 kbps data rate,
>>
>> No, its 500 kilobaud.
>
>It's 500kbps when operating in high density, and 300kbps in
>double-density mode. As the CoCo operates in double density, the 500kbps
>rate is irrelevant.

I have never, and I've dealt with a lot of oddball storage media over the 
years I've been a broadcast engineer, heard of a 300 kilobaud data rate being 
used, in anything.  Whenever there was a shift in data rates, it was to 500kb, 
and then to 1 megabaud for the 2.88 meg 3.5" floppies.

If 300 kbaud was what it took to make it work, the 1773 family CAN do that, 
but ALL the controller conversions I've seen use a different chip and run it 
at 500 kbaud. Std DD floppies turn 300 rpm, the special 1.2 meggers turn 360 
rpm, which is why the otherwise identical 96 tpi drives will not give you 1.44 
megabytes of storage, but only 1.2 megs.  Driving them at 500 kilobyte data 
rates, at 300 rpm, should give you the full 1.44 megs.  And that is a direct 
scale.  If I had ever built one of the hi-dens I could easily prove that.  
Running the math the other way, if the data rate for a 720k, 250 kilobaud disk 
was switched to a 300 kilobaud rate, the disk capacity would only be 864 
kilobytes, not 1200k.

I don't know who this Dave Dunfield is, but he is flat wrong on that point.


>See the following page written by Dave Dunfield:
>
>http://www.classiccmp.org/dunfield/img41867/speed300.htm
>
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