Substituting DSHD for DSDD disks (or DS2D if you prefer)

[Jerome H. Fine]

 >Paul Berger wrote:

> >On 2015-10-26 11:38 AM, Jules Richardson wrote:
>
>> >On 10/24/2015 09:14 PM, Fred Cisin wrote:
>>
>>> Are we really running short of "720K" floppies?
>>
>> I went around all the local places that I could think of a couple of 
>> years ago and bought up whatever stock of floppies that I could find 
>> (and picking sure were slim). Quite a few boxes of 3.5" HD, a few 
>> boxes of 5.25" DD, but zero 3.5" DD and 5.25" HD.
>
With regard to 5 1/4" DD media, a couple of decades ago, I rescued a few 
hundred
RX50 type media from a DEC system which I have not had a chance to look at.
Eventually, they will hopefully be copied at which point they could be 
made available
for the postage to send them.  Note that I am in Toronto (M2R 3G3).  So 
please
send a note if this media is still needed and I will be sure to hold 
onto the floppies.
NOTE that all are obviously USED.

>> 3.5" HD media just killed off the use of 3.5" DD and 5.25" HD, I 
>> suppose. I'm not sure what the reason for my finding a few boxes of 
>> 5.25" DD was, though - perhaps it was just produced in sufficient 
>> volume for there to still be a few survivors kicking around.
>
I also have a few dozen 5 1/4" HD floppies which are also DEC RX33 media
along with a few dozen 3.5" HD media which are also DEC RX23 media.
These RX23 media still be available in reasonable quantities since they were
probably the last of the floppy media which was widely used when a 3.5" HD
floppy drive was still a popular item.  NOTE that all are obviously USED.

>> I've never had any luck finding used disks anywhere locally; people 
>> are a bit too concerned about data theft these days, and all of that 
>> seems to go straight to landfill.
>
> Not long ago I bought a 100 from floppydisk.com for use with my 
> vintage HP's they where reputed to be used but looked like new to me.  
> They seem to work fine, I have not had any fail to format or fail in use.

I am not interested for myself, but which type of floppy media were they?

I probably have about 500 hundred 8" floppy media some of which
are already LLF (Low Level Formatted) to the IBM standard of
SSSD or 488 blocks.  A few have even been LLF with DSDD
(Double-Sided, Double-Density) even though they have only the
Single-Sided Index hole since I have a switch on my DSD 880/30
which supports using an 8" floppy that has the Single-Sided index
hole as an 8" Double-Sided floppy.  In DEC naming convention,
a SSSD 8" floppy is an RX01 LLF, a SSDD 8" floppy is an RX02
LLF and a DSDD 8" floppy is an RX03 LLF.

The DSD 880/30 has a single RX03 floppy drive.  The DPDT switch
which I installed supports the use of an 8" floppy with the index hole
in the Single-Sided location to be used and detected by the RX03
drive as if the index hole was in the Double-Sided position - which
avoids the need to punch a second pair of holes.

For those individuals who are using RT-11, my DYX.SYS (RX02
device driver) supports the use of a bounce buffer which is required
when the user buffer is in Extended Memory above the 256 KB
boundary.  I have mentioned this in the past, but it seems that no
one uses the DYX.SYS under RT-11 any more.  In an emergency,
it is always possible to use DUP to copy the complete floppy media
to a small 512 KB file on a drive which supports 22-bit user addresses
which is usually available at least on the system drive for RT-11 to
be able to run a virtual job that requires low memory overlays.
Note that this DYX.SYS is not ready for general release since it still
does not make use of Extended Memory instead of a very large
buffer in Low Memory.  But in an absolute emergency, it could still
me made available.

Jerome Fine