[Coco] 5 1/4" drive

[Christian Lesage]

Gene Heskett wrote:
> 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.
>   
He is not wrong at all, and neither are all the people who wrote about 
this fact. Please do some googling. Let's put it that way:  You format 
and write to a double-density disk in a 360KB disk drive. The drive 
spins at 300RPM and the floppy disk controller feeds it with a 250kbps 
data stream. Now, you take the same disk, and put it in a 1.2MB drive, 
which spins at 360RPM. What happens to the data rate? The RPM is 
increased by 20%, and so is the data rate. 250kbps x 120% = 300kbps.

You are absolutely right when you say that a 5.25" HD drive would be 
able to format a 1.44MB disk if it spun at 300RPM, but that's not the 
point we're discussing. You are also right when you say that switching a 
720KB drive from 250kbps to 300kbps would result in a 864KB format... 
However, it is irrelevant because (as I already mentioned twice, and we 
both agree on this fact) 5.25" HD drives use 500kpbs for high density 
(and 300kbps for double density).