Re: Did Commodore cheat with the quad density floppies?

On 05/01/2019 21:13, Mia Magnusson wrote:
> I've never ever heard of any useage of MFM or GCR on non-analogue
> transmissions.

Everything is analogue, even ram.

> You could say that MFM also uses the phase of the signal while GCR
> doesen't, and therefore the same media can be used for MFM at double
> the clock frequency than GCR, as the doubled clock frequency for MFM is
> only used for making phase shifts possible but not actually a higher
> signal frequency.

Right, if you only include the drive mechanism and media in your 
costings then MFM is a free way to double your storage compared to FM.

But if you're starting from GCR and costing what it will take to switch 
the digital electronics to MFM for such a small gain, then it's very 
expensive.

It depends on where you start from, if you have plenty of free bandwidth 
to achieve MFM on the electronics side then your design was unbalanced 
to start with.

I'm sure the guy working for the FM controller chip company that came up 
with the idea of an MFM controller chip (which could work with existing 
hardware) got a huge bonus.

> It requires HD media and achieves a worse result than MFM (Amiga MFM 22
> sectors per track).

I am not sure it needs HD media, or whether the drive detecting the 
notch in the HD media affects the filtering.

It is worse than MFM 22 sectors per track, but to achieve those extra 3 
sectors per track needs double the rate.

Which commodore unfortunately implemented using a half speed motor, 
which makes the drives rare as hens teeth.

Not exactly efficient.