anyone familiar w/640kb 5 1/4" format?

[Geoffrey Reed]

On 3/18/11 12:13 PM, "Tony Duell" <ard at p850ug1.demon.co.uk> wrote:
> SNIPPAGE
> 
> If so, you certainly don;t want to be using the high density disks. Their
> coercivity is too high.
> 
> I have had problems using PC '360K' disks in 80 cylinder drives. I am not
> sure why, but some do not format reliably. It may be something like a
> higher noise level on disks not required to handle 80 cylinders.
> 
> I was given a large bag of bluk-erased DEC RX50 disks (which were
> origianlly 80 cylinder signle-sided), and have never had any problems with
> those, not even using both sides.
> 
> Of coruse, there may be a problem with your disk controller or drive.
> 
> -tony


I have to agree with tony on  a couple things :)

1:  don't use High density disks, if you DO get them to format, the data
retention is coing to be short lived generally.

And 

2: there may be something wrong with the controller or drive. :)

I rarely have trouble though using 40tk DSDD media in 80tk DSDD (or QD as
some call it) HOWEVER I NEVER use media that is currently holding a 40 track
format.  If all I have is 40tk DSDD formatted media, it goes visiting the
degausser/bulk eraser.  I have had lots of problems using non bulk erased
media that HAD been formatted 40tk DSDD in 80 track drives (dec-rainbow
RX50, Altos (can't remember model, but it used 100tpi 80 track drives IIRC
and ran CP/M) or even on a 286 or better formatting the media out to 720K in
a 1.2M drive.

So...

If it ain't formatting reliably, bulk erase the hell out of the 40tk DSDD
media and it -should- format out fine to 80 track DSDD.  I saved a LOT of
money by using the "40 track" media.  A friend working at Verbatim (IIRC)
many moons ago told me their "dirty little secret", all of their low density
media was designed to go 80 track, once there was > certain percentage
failure rate during testing, possibly 5%, don't remember for sure, the media
was 'certified' as 40 track and packaged as such.  But that is pretty much
the same way the ram manufacturers rated their DRAMs speed wise :)