Re: Extracting files off “unknown” 8 inch disks. Any thoughts…

allison allisonportable at
Thu May 4 20:05:39 CDT 2017

On 05/04/2017 06:35 PM, Fred Cisin via cctalk wrote:
> On Fri, 5 May 2017, Terry Stewart via cctalk wrote:
>> Yes, reading them with IMD was one of the first things I tried. 
>> Couldn't
>> do it at all.  Tons of errors, no tracks could be read.  IMD didn't
>> recognise the layout at all.
>> All the disks I tried were like this.
> Then, either it is impossible to read with the PC FDC, or we missed
> something.
> Is your 8 inch setup capable of FM/single density?
> I think that Dave has a utility to test that.
> Do you have access to any sort of "flux-transition" device (Central
> point option board, cat-weasel, kryoflux, etc.)?

First if they are DEC its one of two formats either FM aka RX01 or FM2
aka RX02.

RX01 base format is 128byte sectors and 26 per track  PC can read them.

RX02 base format is 256 bytes per sector byte the timing encoding is
unreadable with any LSI controller.  It uses FM headers to confuse the act.
To read that you need:
- RX02 and a compatible system.
-  one of the many DEC clones (DSD, and many others usually using 8X300
family chips)  in a DEC box (and cpu).
-Catswesel or one of the other flux readers in a PC.

Note the RX02 drive is dual format, it can read/write rx01 media ( 8"
SSSD).  It can also read and write
RX02 format or "init" RX01 media to RX02 format and back to RX01.   RX02
format was unique to DEC
and the only other that could read or write it were DEC hardware
compatible controllers.

First you have to satisfy the first (able to read sectors) to do the second.

Then the possible 8" ODS formats are....

DEC format (RX01 or 2) include PDP-8 family mostly OS8 (odd 12bit

The  PDP-11 group  RSX, RSTS, RT11, unix, are most common.  Note PDT150
is also PDP-11 RX01.
This was the most likely and populous hardware group using RX01/2 disks.   
The Qbus PDP-11 systems could also support RQDX controller for 5.25 and
3.5 inch floppies. That made later systems with RX01/02 less common over

VAX, 11/78x uses a PDP11 (LSI11) to load microcode.  It is PDP11 and
RX01 media.
Most of the later systems *if* they have 8" RX drives are likely any
format compatible with
the PDP-11 group as that's the likely exchange partner/target. 

I've not seen VAX format on RX01/2 media, its not impossible except for
the VAX78x family
as the PDP11(lsi-11) physically own the drive.   To do that it had to
have a unibus  RX controller
and a RX01/2 drive and then the file format can be anything as VMS had
utilities for most all the
PDP11 formats.

Latter vaxen used RL02 or TU58 or other media to load microcode.  
Microvax and later machine
did not load microcode save for exception code during the normal boot
sequence.   In those
cases a RX01/2 was unusual to the extreme save for maybe a Qbus microvax
(not a supported config)
assembled as a hack.  Most of the Qbus VAX systems with floppy used
RX33(5.25" RX50) or RX23(3.5")
as the RQDX1/2 controllers supported 5.25" floppies initially and later
firmware supported 5.25" Teac 
and 3.5" Sony drives as well.  RQDX3 5.25" Teac and RX50  and 3.5" Sony
drives.  Because of this
and far more space per drive RX01/2 was rarely used.  The RQDX
controllers could do the stated
floppies even is MFM  disks were not connected. 

Also the VAXes may have run unix and that was likely user save media.

in short if RX01 anything that can read SSSD 8" is good enough.  IF RX02
a pdp11 and RX02(or third party
equivalent) makes it easy.    To do RX02 on PC you must have a flux
reader, 765 and later clones cannot.

How do I know.  I have PDP-8, PDP11 (with RX02) and VAX (qbus uVAX,
uVAX2000, and 3100 family).
I used to and still do exchange between RT-11 and CP/M using RX01 mode
and a CP/M utility that
knew RT11 format.  IF it was RX02 media, I'd rewrite on the PDP11 to
RX01 media using FIT or other


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