22 Nov
2014
22 Nov
'14
10:09 p.m.
On 2014-11-22 17:14, Jerome H. Fine wrote:
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"?
The RX02 is not a standard double density floppy. It is a single density
format floppy with a double density encoding for the data area of each
sector. That is a very different thing.
I have double density IBM floppies at home, and believe me, I have tried
using them in RX01 and RX02 drives. They obviously do not work.
But it should be obvious even without much more than a cursory glance at
the documentation for an RX02. There is no contradictions to what DEC
documented compared to what I wrote.
DEC RX02 floppies are really the same low level format as RX01 floppies.
There is a bit in the sector header for each block that is set to 1 if
the sector is actually in double density for an RX02, or 0 for single
density. I don't know if IBM themselves ever used that bit in the sector
header for anything, but DEC used it for this purpose, and it
documented. You can, on a per sector basis, use either single density or
double density. The low level format is always the same.
Johnny
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.