8" Floppies

From: Richard Erlacher <edick_at_idcomm.com>
Date: Fri Aug 31 09:41:31 2001

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

----- 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 - 09:41:31 BST