Imaging RX02 disks for simh (was: Re: MU-BASIC V2 and RT-11 V03B distribution disks.)

Jerome H. Fine jhfinedp3k at
Sun Mar 6 22:24:14 CST 2016

 >Brian Walenz wrote:

>How the heck do you copy an RX02 disk for use in simh?
>I've been trying to transfer RX02 images between simh and a real PDP11
>(that has only two RX02's, console, and ethernet).  So far, I've only
>attempted sending an RX02 image from the PDP to simh, but simh fails to
>read it: "?DIR-F-Invalid directory".  Even after adding 13*512 bytes to the
>start for the missing track, I still get invalid directory.
In order to verify how an arbitrary container file is handled under SimH, I
attempted to run V3.9-0 under Win98SE.  I doubt that the actual Windows
operating system makes a difference, but just in case.

I was able to boot RT-11 using an MSCP device for which:
When I arrived in RT-11 after having booted on FRQBAR.DSK,
performing the RT-11 command:
provided all zeros in the dump output of block zero.
Further, when I attempted to use RY0: which I assume is the
device name for RX02 images, all the attempts were rejected.

On the other hand, when I used Ersatz-11,
when I arrived in RT-11 after having booted on FRQBAR.DSK,
performing the RT-11 command:
the expected values were displayed in the dump output of block zero.
Further, when I attempted to use DY0: which is the device name
under Ersatz-11 for RX02 images, everything worked as expected.
More to the point, I was also able to:
MOUNT  DU1: FRXBAR.DSK /RO   (Ersatz-11 allows access to
using both DU: and DY: emulation at the same time when the access
is READ  ONLY), and determine that  both DU1: and DY0: were
identical when I used BINCOM to compare both RT-11 devices.
All 988 blocks of both DU1: and DY0: could be read and were
found to be the same.  Obviously, that was expected since the
same container file was used in each MOUNT command.  But
the fact that Ersatz-11 is able to access FRXBAR.DSK and
SimH is not able to do so is what is so confusing.

One minor point that seems worth while to mention is that the
Ersatz-11 emulation for the DY: (DEC  RX02 device) also
supports DSDD media which have 1976 blocks and with
a suitable floppy drive and controller support double-sided,
double density operation, or what DEC intended to be the
RX03 floppy drive.  While it seems that DEC never sold
such the RX03 hardware, there was code in V04.00 of
RT-11 to make the attempt to support double-sided media
as a SYSGEN option.   Unfortunately, the code that was
released with V04.00 of RT-11 was not quite correct.  By
V05.00 of RT-11, the code to support double-sided operation
had been removed.  However, at the very least, an RX03
floppy drive was produced and sold by DSD (Data Systems
Design) and sold as the DSD 880/30.  Again unfortunately,
the controller supported only 18-bit hardware addresses
which required an enhancement of the DYX.SYS device
driver to support all 4 MB of memory for user buffers.
I have mentioned this enhancement a few times, but there
seems to be zero interest.

Since I don't have access to the SimH manuals at the moment, I
don't know what I am doing that is incorrect.  But since I have
never attempted to use SimH before with either RX01 or RX02
images, there might be other problems.

I hope that the above information helps.

I would appreciate any information in respect of using the TCP/IP hardware
and software to access a Qbus PDP-11 via ethernet, and especially from
a system running RT-11 and / or TSX-Plus under both SimH and Ersatz-11.

>My process is to COPY/DEVICE/FILES DY1:/START:0/END:330 DY0:BLOCK1.DAT,
>then FTP that off the PDP, delete the file, and do the remaining two thirds
>of the disk.  Once all are transferred, "cat *DAT > floppy.dsk".
The RT-11 commands are correct.  Why SimH has difficulty is
not understood.

>I can transfer RX50 images using the same recipe, though I haven't tried
>sending an RX50 image created on simh back to the PDP.
>For what it's worth, I'm having the same problem with Alan Baldwin's TCP/IP
>disk images from  simh can't read the
>individual DSK images, but could read the *.PKG with the disks inside, and
>from that, I could (RT-11) MOUNT each disk to a logical device.
I recognize some of the details of what you are doing, but I have no
idea of the actual hardware and software that you are using.  I would
like to use TCP/IP to move files backs and forth under RT-11, but I
don't know what hardware is needed, especially if there are to be
transfers between RT-11 running under SimH or Ersatz-11.  I do
have a router between two of my Windows systems, so that part is
already working.  But I am quite sure that the speeds between the
Windows systems and the PDP-11 don't match at all.

Of late, I have found that working on the RT-11 Symbolic Debugger,
SDHX.SYS to be specific under a Mapped RT-11 Monitor to be
sufficient challenge to keep me busy.  Version Y01.16 has a few
bugs which need to be fixed.  There are also some enhancements
that will, hopefully, improve its use.

Jerome Fine

>>On Thu, Jan 28, 2016 at 11:50 AM, Mattis Lind <mattislind at> wrote:
>>I found some 8 inch floppies with distribution kits for MU-BASIC V2 and
>>RT-11 V03B. I imaged those and put them here
>>if anyone is interested in playing with MU-BASIC. There are both RAW disk
>>images and to be used in SimH and like and also DMK/IMD files.
>>The system that floppies came with is this little (
>>system once used at Scania in Södertälje.

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