Copying DEC VAX set up disks rx50, help

Ethan Dicks ethan.dicks at
Sat Mar 3 23:07:11 CST 2007

On 3/3/07, g-wright at <g-wright at> wrote:
> Hi,
>  I have a stack of  the orginal VAX  Disks (console and
> set up , 5 1/4 RX50 )  The ones in front of  me are
> for a 8200 series.   I would like to copy them but  can't
> get image disk to work. Is this possible or do I have to
> use a VAX..

You should not have to use a VAX.  There's nothing strange about the
low-level format for 8200 console disks (I have an 8200/8300 in my
basement, FWIW).

> I  have RT11 on a micro PDP-11 with a RX50
> and I think my professional still works.   But would  really like to
> get it on a better media for long term storage.


> Image Disk reads it with out errors
> 0/0: 300k DD 10 sectors of 512 bytes - G1:9 G2:17
> 0/1: Single sided
> 0/0: Single Step
> 800 sectors (800 data, 0 compressed, 0 unaval)
> Read complete

So far, so good...

> Trying to write and it has errors from the get go.
> 0/0: 300k 10  sectors of 512 bytes
>  :format error <0> overun
>  :write error    <2> no sector
>  and on .............................
> written on a PC with 1.2 HD drive
> Tried on another 1.2 and on a 360k drive
> all capable of SD .
> I tried  both HD  and DD  disks . all bulk erased first.

Hmm...  Others on the list can chime in with their floppy expertise,
but from the way you are describing what you've tried, it doesn't
sound as if you have a clear picture of the media in front of you.

RX50 disks are single-sided (as mentioned by imagedisk in your read
example, above), 80-track, ten 512 byte-sectors per track for a total
of 400Kbytes.  Your 360K drive can _not_ write RX50 disks (among other
issues, it's a 40-track drive).

If you've verified that your 1.2MB drive works as a PC drive, then,
presuming you have the right media, you shouldn't have any hardware
issues writing RX50 images.  Media is where I get a little fuzzy on
the details.  I've personally only ever written RX50 images to RX50
media.  I've never tried to recycle PC floppies, so I'm not sure what
the best choice is.  I do seem to recall that what you want should
*not* have hub reinforcement rings, as they can cause alignment
problems in real RX50 drives.

If you can score a Teac FD55GFR drive, it can be strapped up to be a
_real_ RX33 or strapped to behave "normally" on a PC FC controller.
The strapping has to do with motor on and select lines, not data, BTW.
 I mention the FD55GFR because it was the 5.25" drive DEC shipped
after they moved on from the RX50, so you can be sure that you aren't
having hardware compatibility issues (plus, it's all-around good,
solid 5.25" drive).

In your case, I'd run some read/write/verify tests with your 1.2MB
drive and PC-compatible floppies and if they show any marginal
problems, try cleaning the heads.  You can clean the heads in any
case, but it might be nice to have a "before" picture to compare
post-cleaning performance.  If you can locate some real RX50 media,
try writing to those.  They aren't "magical", but they are
pre-formatted for 10 sectors-per-track (MS-DOS uses 9 sectors for 360K
disks and 17 sectors for 1.2MB disks, if you didn't remember).  As
with the RX01s, most DEC equipment can *not* lay down the RX50
low-level format, the Rainbow being the most notable exception.  A PC
_can_ format an RX50, but you'll need some 3rd-party tool to do that -
DOS can't by itself.

I'm sure others will be able to chime in with various informed opinions.


P.S. - just found this old doc on the state of RX50s and various
versions of DOS and tools for DOS...  Dunno what OS you
are using to write your disks, but perhaps some info in this FAQ will
shed some light.

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