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

allison allisonportable at
Fri May 5 07:19:29 CDT 2017

On 05/04/2017 07:39 PM, Terry Stewart via cctech wrote:
>> And yet, if there were an RX02 somewhere on this VAX, I don't believe
> you'd be able to read them at all... RX02 seeming more likely with a VAX.
> Interestingly PUTR, does seem to accommodate this, and the kind of system I
> have set up (i.e. 1.2 MB 5.25 inch in CMOS even though it's an 8 inch
> drive).  From the readme file...
> "SET x: type
>         Sets the drive type for one of the four possible PC floppy
>         drives A:-D: (note that actual PCs rarely have more than one or
>         two floppy drives).  The type must be RX01, RX02, RX03, RX50,
>         RX33, RX24, RX23, or RX26.  The default value for each drive is
>         whatever was stored in CMOS memory by the ROM BIOS setup
>         utility.
Yes but RX02 uses FM headers and FM2 sectors.  NO FDC CHIP CAN READ THAT.
None of the 765 family or WDC 179x and cousins can.

It was unique to DEC though Intel did similar but not the same on the
MDS800 dual density drives their difference was the whole media
was one recording format either single or double density.

You need a PDP11 with RX02 (or DSD880) or a catsweasel.

I know this as I have the former. 


>         This command may be useful when the drive types stored in CMOS
>         RAM are incorrect for some reason.  It's also helpful when an 8"
>         drive, or a real DEC RX50 drive, has been attached to the PC
>         using a D Bit "FDADAP" adapter, or something equivalent.  There
>         is no standard for representing these drive types in CMOS RAM.
>         Using real RX50 drives (or other 300 RPM quad-density drives
>         such as the Tandon TM100-3 and TM100-4) is different from RX33s
>         (which is what PUTR calls regular PC 1.2 MB drives) because the
>         motor speed is slower, so the FDC chip must be programmed for a
>         lower data rate to match."
>  I didn't spend too much time on PUTR as it seemed to be more for the older
> DEC OSs rather than Vax VMS.  VMS wasn't mentioned as an option in PUTR
> which is why I spent more time experimenting with ODS2, which was VAX
> specific. I said, PUTR tries to figure out what DEC OS (if any)
> is on the disk and failed to find one.
> Maybe I should play around with the switches in PUTR more before I give up
> though....
> Terry

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