21 Nov
2014
21 Nov
'14
12:57 p.m.
On 11/21/2014 2:26 PM, Glen Slick wrote:
Is it correct that RX01 format floppies can be created
from blank
floppies with a standard PC floppy controller (or at least some
controllers / motherboards, depending on the controller chip) while
RX02 format floppies cannot?
My understanding (perhaps incorrect, if so, someone please correct me) is that
the wart-level-detail answer to this question is that '_blank_ RX02 floppies
can be created on anything that can create RX01 floppies', but that RX02
floppies _with data on them_ can only be created on RX02 drives. I.e. an RX02
is fed RX01 floppies, which it then writes in the unique-to-DEC double density
RX02 format. (As Chuck explained, the _headers_ are in the standard IBM form,
but the _data_ part of the sectors is written in a DEC-specific double-density
format.)
Noel
21 Nov
21 Nov
1:04 p.m.
My understanding (perhaps incorrect, if so, someone please correct me) is that
the wart-level-detail answer to this question is that '_blank_ RX02 floppies
can be created on anything that can create RX01 floppies', but that RX02
floppies _with data on them_ can only be created on RX02 drives. I.e. an RX02
is fed RX01 floppies, which it then writes in the unique-to-DEC double density
RX02 format. (As Chuck explained, the _headers_ are in the standard IBM form,
but the _data_ part of the sectors is written in a DEC-specific double-density
format.)
Almost, at least to the user.
An RX02 drive can reformat an RX01 disk as RX02. What it can't do is format
a blank disk. So if you make an RX01 formatted disk (essentially possible on
any machine with 8" drives that supports an FM (single density) format, then
the RX02 can turn it into an RX02 disk.
Incidentally, there were Qbus cards (I have never seen a Unibus one) to
handle RX02 disks using normal 8" (Shugart 800, etc) drives. Some of those
I think could format a totally blank disk.
-tony
1:23 p.m.
On 2014-11-21 12:57, Noel Chiappa wrote:
Pretty much correct.
You could also say that there is no RX02 format. You cannot format a
floppy in RX02 format.
An RX02 floppy is formatted the same way as an RX01.
When an RX02 drive want to do double density, it just writes a bit in
the sector header saying that this sector is in double density, and the
actual data part of the sector is written in double density. The format
of the floppy as such is still the same as an RX01.
And of course, an RX02 reading that sector will notice the bit in the
header saying that it is double density, and will read the actual data
part of the sector in double density mode.
So, any floppy that you use in an RX01 or RX02 is *always* formatted as
an RX01. Which is the same as the original IBM SD SS 128 bytes per
sector format.
Only an RX02 can actually do the DEC double density format as done by
the RX02. You cannot read that floppy on other drivers with other
controllers generally, since they aren't actually capable of switching
between different densities in the middle of a sector.
But the RX02 is not a separate format as far as the floppy goes. It's
just the data in each sector so written that is "special".
Johnny
On 11/21/2014
2:26 PM, Glen Slick wrote:
Is it correct that RX01 format floppies can be
created from blank
floppies with a standard PC floppy controller (or at least some
controllers / motherboards, depending on the controller chip) while
RX02 format floppies cannot?
My understanding (perhaps incorrect, if so, someone please correct me) is that
the wart-level-detail answer to this question is that '_blank_ RX02 floppies
can be created on anything that can create RX01 floppies', but that RX02
floppies _with data on them_ can only be created on RX02 drives. I.e. an RX02
is fed RX01 floppies, which it then writes in the unique-to-DEC double density
RX02 format. (As Chuck explained, the _headers_ are in the standard IBM form,
but the _data_ part of the sectors is written in a DEC-specific double-density
format.) 
2:23 p.m.
On 11/21/2014 01:23 PM, Johnny Billquist wrote:
Only an RX02 can actually do the DEC double density
format as done by
the RX02. You cannot read that floppy on other drivers with other
controllers generally, since they aren't actually capable of switching
between different densities in the middle of a sector.
Another good reason to have a Catweasel controller in your stable of PC
accessory cards. I think that Tim Mann(?) wrote a package to handle the
RX02 DEC double-density format. At least I recall using a set of CW
utilities to dupe some RX02 double-density floppies.
--Chuck
3:42 p.m.
On Fri, 21 Nov 2014, Chuck Guzis wrote:
On 11/21/2014 01:23 PM, Johnny Billquist wrote:
Right, you are:
http://tim-mann.org/catweasel.html
Mike Loewen mloewen at cpumagic.scol.pa.us
Old Technology http://q7.neurotica.com/Oldtech/
Only an RX02 can actually do the DEC double
density format as done by
the RX02. You cannot read that floppy on other drivers with other
controllers generally, since they aren't actually capable of switching
between different densities in the middle of a sector.
Another good reason to have a Catweasel controller in your stable of PC
accessory cards. I think that Tim Mann(?) wrote a package to handle the RX02
DEC double-density format. At least I recall using a set of CW utilities to
dupe some RX02 double-density floppies.
3689
days inactive
3689
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