Re: Did Commodore cheat with the quad density floppies?

On Thu, Jan 3, 2019 at 2:51 PM Mia Magnusson <mia@plea.se> wrote:
>
> Den Wed, 02 Jan 2019 15:34:24 +0100 skrev André Fachat <afachat@gmx.de>:
> > Hi there,
> >
> > I was looking at floppy disk recording schemes and I am wondering if
> > the 8050/8250/1001 floppy disk format with over 500kB per side was
> > actually out of spec of even the Quad Density disks?
> >
> > The recording frequency was increased from 250kHz to 375kHz (× 1.5,
> > for the innermost i.e. most critical track/speed zone). That resulted
> > in a much increased number of bits per inch. See here:
> > https://extrapages.de/archives/20190102-Floppy-notes.html
> >
> > What do you think?
>
> Afaik the 8050/8250/1001 drives are supposed to use "QD" disks, which
> seems to be a format that's supposed to handle a higher density than DD.

"QD" disks have the very same 300 oersted magnetic media as SD/DD disks,
it was only the mechanics and R/W heads that allowed to use more
effectively the storage media.
Later HD drives used different R/W heads (or different currents) and
required 600 oersted media, doubled bitrate to 500 Kbps and changed
speed to 360 rpm.

At the university, we had a few Olivetti LSX-3005 that were equipped
with 96tpi 5 1/4" drives (QD, not HD obviously),
I remember nobody ever tried to find "QD" disks, normal DD 48TPI disks
were used (albeit I remember good quality brands were purchased
usually, like 3M, Olivetti).

> It seems common for people to think that QD was a marketing thing used
> for 96TPI DD disks, but I've seen so many 96TPI disks marked DD and

again, 96TPI DD is just the same media as 48TPI DD, just maybe tested
better (or just advertised as 96TPI, who knows).

> only a few (like one or two, and it was last summer that I first saw
> them) disks actually labeled QD. (They contain a book keeping software
> package, in Swedish, from the Swedish Commodore importer Datatronic.
> Will be preserved as soon as I get my 8050 up and running, which has
> been waiting a while for me to find my stash of IEEE cables :) )).
>
> It would be really strange if floppy media didn't evolve the same way
> as magnetic tapes did. With media good enough for 250kHz at track 35
> when the 5.25" floppys were new, and soon good enough for 250kHz at
> track 40, it seems reasonable that some years later the media used for
> those drives were actually good enough for 375kHz at the 48TPI
> equalient of track 35, which almost is where the highest track number
> on a 77 track 100 TPI drive will end up.

I really think the better Kbps rating is due to the use of the more
efficient GCR code instead of the MFM.

>
> (At some point in time a market for cheap rather crappy disks seems to
> have evolved though, but those were probably anyway nothing people used
> in their 8050/8250/1001 drives).
>
> (Everyone who's been around long enough to remember cassette tapes from
> the 70's and the 80's remember that before tapes like Maxell UD and
> similar the standard / ferro / type I tapes did really sound crap with
> a high noise level and muffled treble. Then something happened in the
> late 70's and early 80's, resulting in more and more kinds of tapes
> getting a lot better, and at the start of the 90's basically almost all
> tapes had a decent sound even though there were of course still
> differences between them).

There're two different issues on compact cassette:
1) different (really much different) magnetic media, type I (Fe2O3,
iron oxide), Type II (CrO2), type III (FeCr), type IV (metal), these
media required different equalization and different recording
currents. Type I are usually very bad sounding and noisy, type IV have
the best quality, but the recorder really NEEDS to know what type of
tape it's trying to record into, otherwise you wouldn't get much
better results, unless maybe a bit less noise if you use a type IV
tape on a old, low quality recorder.
2) Dolby NR pre/de-emphasys. These noise reduction techniques have
been introduced starting from 1965, last one afaik was introduced in
1986. Not all recorder were equipped with these circuits. A type I
with the best NR circuit could sound really better than a type II with
no Dolby.
So, all in all, nothing in common with floppy disks :)

Frank