Re: Did Commodore cheat with the quad density floppies?

Den Sun, 6 Jan 2019 16:19:33 -0500 skrev "Mike Stein"
<mhs.stein@gmail.com>:
> 
> ----- Original Message ----- 
> From: "Mia Magnusson" <mia@plea.se>
> To: <cbm-hackers@musoftware.de>
> Sent: Sunday, January 06, 2019 9:17 AM
> Subject: Re: Did Commodore cheat with the quad density floppies?
> 
> > ... Maybe the 8050 were one of the first drives to have a smaller
> > head gap than most DD drives did?
>  
> There were a number of other systems around since the late 70s that
> managed to get close to 500KB/side formatted capacities out of DD
> disks using various techniques including GCR, more bytes/sector etc.;
> I'm not aware of anyone else other than Apple using zone recording
> but these were the wild west days of incompatible disk formats, so
> anything is likely...
> 
> Micropolis, who supplied many of the drives in the 8050, was one of
> the first to go to a higher TPI (100) than the then standard 48 TPI;
> Tandon and MPI also made 100TPI drives, but in the end 80 tracks at
> 96TPI became the 'QD' (and HD) 'standard' since that also made
> reading and writing 48TPI diskettes possible by double-stepping.
> 
> Interesting side note: rarely seen outside of Japan, but some
> manufacturers used exactly the same format in all diskette sizes (8",
> 5.25QD/HD and 3.5") which is why you'll find options on some 5.25"
> and 3.5" drives to select the 8" standard 360 RPM instead of 300. 

Interesting.

> 5.25" HD drives normally run at 360RPM; many have an option to select
> 300 RPM, but compatibility with DD and QD disks is usually achieved
> by changing the transfer rate instead.

The 360 rpm on those drives must had been to make them more of a
drop-in replacement for 8" drives. 



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