Re: CBM-900 floppy disk format/encoding

----- Original Message ----- 
From: "Groepaz" <groepaz@gmx.net>
To: <cbm-hackers@musoftware.de>
Sent: Friday, October 28, 2011 10:42 AM
Subject: Re: CBM-900 floppy disk format/encoding


> On Friday 28 October 2011, you wrote:
>> I have checked a number of sources on the internet.  There does not seem
>> to be any agreement on what the track density of quad density is.  Some
>> say 48 tpi, others 96 tpi.  96 tpi seems to be in the majority.
>
> 100tpi

-------------------

Only in the closed world of Commodore and a few other vendors (e.g. Vector
Graphic).

The QD 'standard', such as it was, was the same as the more modern HD
drives, i.e. 96TPI, which meant narrower heads and stepper motors/mechanisms
that took twice as many steps as DD drives for the same distance but with
the read/write electronics and RPM the same as DD drives (300); thus, unlike
100TPI drives, there was backward compatibility since both types could also
read and write 48TPI DD disks by simply double-stepping the head(s).

The difference between 96TPI QD and HD drives is that HD drives can use
either DD/QD or HD by selecting two different read and write parameters to
accommodate the two different diskette types and their different magnetic
properties (usually with pin 2 of the interface); many HD drives also have
dual-speed (HD's 360RPM vs DD/QD's 300RPM) capability, but 300RPM can also
effectively be emulated by changing the rate at which data is transferred
to/from the diskette (as in the PC for instance).

m


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