8" Floppies

From: Don Maslin <donm_at_cts.com>
Date: Fri Aug 31 15:52:54 2001

On Fri, 31 Aug 2001, Richard Erlacher wrote:

> Well, if the written spec's can be believed, you can't SEE the difference
> between DD and SD media. That doesn't change the fact that they have different
> spec's. Further, DS media are certified on BOTH sides, while the emulsion on
> one side may be defective.
>
> It's true that DS media have their index hole located differently than SS media.
> The index timing is different, according to some drive makers, albeit not VERY
> different. At least one mfg spec's the DS drives with 160 microsecond +/- 50
> from the start of /Index to the data burst, while SS media are at 200. I've
> never given much thought to this and how it affects things, but I am not
> comfortable with the notion of switching, mechanically, between the two sensors.
>
> Dick

Probably of little consequence, Dick, since his DSDD disks will not be
readable by anyone else unless the have performed the same modification
to a single-sided drive.
                                                 - don

> ----- Original Message -----
> From: "Jerome Fine" <jhfine_at_idirect.com>
> To: <classiccmp_at_classiccmp.org>
> Sent: Friday, August 31, 2001 7:42 AM
> Subject: Re: 8" Floppies
>
>
> > >Absurdly Obtuse wrote:
> >
> > > For those who asked, I need DSDD 8" Soft-Sectored Disks.
> >
> > Jerome Fine replies:
> >
> > I don't know if this will help, but here goes.
> >
> > I was using the DSD 880/30 - an RL02/RX02 compatible. It
> > holds a single 8" floppy drive which can use both SSDD and DSDD
> > diskettes (soft-sectored). I found that since I had a small number of
> > DSDD diskettes and the media seemed to be identical, the ONLY
> > difference that I could observe was that the index hole was in a
> > different location.
> >
> > I wired a DPDT switch into the index hole detection circuit. In the left
> > hand position, it was wired to duplicate the existing circuit. When I
> > wanted to REVERSE the operation, I used the right hand position of
> > the switch. In the second position, the index hole for a SSDD diskette
> > caused the drive to route the signal from the sensor to the portion of
> > the circuit which normally detected the signal from the DSDD index
> > hole. Thus, the drive and the software "THOUGHT" that a DSDD
> > media was present and I was able to use a SSDD diskette as a DSDD
> > diskette without having to punch a second set of index holes. The
> > use of a DSDD diskette as a SSDD diskette is also possible if that
> > is useful - I never found it to be needed.
> >
> > Naturally, this required that I do a LLF (Low Level Format) on both
> > sides of the diskette. This the DSD 888/30 is able to do all by itself
> > and that solved the problem. As for using the DSDD diskette with
> > DEC software, V4.00 of RT-11 had some code which showed how
> > to access the "second" side and use the floppy drive as an RX03.
> > I used that code as a starting point since I also wanted to allow the
> > DYX.SYS device driver in a 22-bit environment with V5.03 of
> > RT-11. Note that the DSD 880/30 and the DEC RX02 with an
> > M8029 can use only the first 1/4 MByte (18 bit addresses) when
> > a transfer is made to/from the DMA silo from/into a buffer in the
> > memory of a PDP-11. Software in the DYX.SYS device driver
> > is able to use all 4 MBytes of the PDP-11 physical address space
> > in a manner totally transparent to the user of the device driver.
> >
> > I realize that Sridhar is not using RT-11, but I just thought I might
> > mention the above for those of you that do.
> >
> > Sincerely yours,
> >
> > Jerome Fine
> >
> >
>
>
Received on Fri Aug 31 2001 - 15:52:54 BST