RX01 Floppies

Jerome H. Fine jhfinedp3k at compsys.to
Sat Nov 22 19:14:49 CST 2014

 >Johnny Billquist wrote:

> >On 2014-11-21 19:48, Jerome H. Fine wrote:
>> I should have realized that the situation needs to be clarified:
>> (a)  As far as I know, (almost?) all soft sectored 8" floppy media
>> are formatted as either single-density (which is the IBM standard -
>> also known as the DEC RX01 option) or double-density.(which
>> is the additional DEC RX02 option).  In the latter case, the format
>> is essentially the same, but only the data portion of the sector is
>> double-density.  In addition, while a DEC RX01 drive can use only
>> single-density media, a DEC RX02 drive can use BOTH single-
>> density (SSSD) AND double-density (SSDD) media which means
>> that the DEC RX02 drive can read / write media from a DEC RX01
>> drive - but can boot an RX01 media only if the boot block is first
>> changed from DX to DY. 
> Incorrect. The RX02 cannot read standard 8" Double Density floppies. 
> It can only deal with single density floppies, just like the RX01.

I am quite sure that your information with regard to Double-Density
floppies is technically correct.  Your much greater level of experience
must have acquainted you with actual double-density floppies at some
point.  However, it would be helpful if you could provide a specific
example of a real double-density 8" floppy so that we can all share
the same information.  The information which would be needed is
the name of the manufacturer of the floppies, the name of the computer
system, the name of the double-density drive, the name of the controller,
the name of the operating system and the name of the device driver used
when a "standard 8" Double Density floppy" is present.  If you don't have
all of the above information, present at least as much as you remember.

Also, at least an estimate of the percentage of "standard 8" Double
Density floppies" in use compared to the standard 8" IBM SSSD
floppies (including both DEC RX01 and DEC RX02) would be
useful so we can judge if "standard 8" Double Density floppies"
were significant.  In my opinion, anything less that 1% would be
considered insignificant.

It is great to contradict what all DEC documentation on 8" RX02 floppies
mentions with respect to double-density media (and given that the DEC
documentation was usually complete and correct - DEC, in this case
much have been providing false information or at least characterizing
"double-density" incorrectly at least as far as you are concerned) and I
am sure that you do have some competing example in mind.  What is it?
And why is the statement that DEC makes that the media are double-density
(when the sector size is 256 bytes) "incorrect"?

Jerome Fine

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