CD-ROM on RT-11?

From: Jerome H. Fine <>
Date: Thu Apr 4 08:45:57 2002

>Tom Leffingwell wrote:

> >On Thu, 21 Mar 2002, Jerome H. Fine wrote:
> > If you are going to have a CD on your real PDP-11 with a Qbus host adapter,
> > then if you want to be able to boot partition zero, I suggest you use the
> > command:
> > to the partition you are going to place on the CD. MANY other aspects also
> > need to be considered if it will be a bootable partition.
> I've been out of touch with the list for a little while, so I just got
> this. Anyway, what would the many aspects be? I was operating on the
> assumption that the image I would get or make would have already been
> copy/boot'ed so, it should be a bootable image, and if transferred as an
> exact image to the CD it should work.

Jerome Fine replies:

Since I have used a CD burner for only a month, I was limited to
the experience of using only the RT-11 Freeware CD from Tim

Also, since I had only an IDE CDROM drive on a PC, my experience
using the CD was only under E11 under Windows 95 and Windows 98.

I did try and connect a SCSI CDROM drive to a Qbus CQD 220/TM
on a real PDP-11, but was not able to get it to work.

More recently, I think I have been able to copy a file which had been
tested to see if it could be used to successfully boot RT-11 (under E11
under Windows 98). I copied that file to a CD and was able to "View"
all of the blocks on the CD in their correct locations on the CD using
Nero Burning, but I was still not able to boot RT-11 from the CD.

One key aspect to realize is that RT-11 knows only about blocks
that are 512 bytes. Since a CD has a 2048 byte sector, that problem
must be overcome, but is not the only problem. Fortunately, a CD
is a READ ONLY media, so problems associated with writes
don't ever arise. One problem that RT-11 does not have is that
the drive media is not required to be writable, although there will
sometimes be SWAP errors after a program exits - which can be
avoided by using the command

All I am saying is that a CDROM drive is not a supported drive under
RT-11. And while I am sure that it is possible to write a file which is a
bootable image to a CD, the correct combination of hardware is not
well specified in my mind. If you are actually able to boot RT-11 from
a CD, it would be appreciated if you would tell us the specific hardware
components which you used along with the software version of RT-11.

One aspect to note for V5.03 of RT-11 is that you may be able to read
a non-zero partition, however, the standard DEC distributed MSCP
device driver is UNABLE to boot from a non-zero partition. So if
are used with V5.03 of RT-11, it is impossible to boot from DU1:
using the DEC version of the MSCP device driver. This is not a
problem with V5.06 of RT-11, so obviously it is a software bug.

> I did finally manage to get my RX02's copied to a VMS machine. The guy
> that was helping me (who had the vax/vms machine) was out of town for
> awhile. Anyway, we copied an image of a bootable floppy to the VMS
> machine, and back to a new floppy, which booted fine with no need to
> copy/boot it (since the imagine was already that way). We also used VMS
> exchange to may .dsk files. I need to read up a little more on exchange,
> but I was thinking if I can work with the .dsk imagines of the ftpable
> RT-11 5.03, I should be copy in my program and then copy that to a SCSI
> disk, make sure its bootable, and then make an image of it. The .dsk
> files seem to be little file on file systems as opposed to just making an
> image.

Using Exchange under VMS had certain annoying limitations the last time I
used it. While it was possible to MOUNT the file or the drive as "/FOREIGN",
there was no variable to specify the partition. Thus the default was ONLY
partition zero. It was possible to circumvent this problem with a hard drive
that is also compatible with PDP-11 hardware (the only one I know of
is a SCSI hard drive or a removable media such as Magneto Optical),
but it was not simple.

One problem you may have with the downloaded DEC distribution
of V5.03 of RT-11 is that the boot block zero assumes an RL02
disk drive. If you copy it to an MSCP media, then you must
if you are going to do a hardware boot. However, if you can
first boot from the floppy under V5.03 of RT-11 (which also
poses a problem - but not too difficult), then you can do a
soft boot via the command:
after which you can then set up the boot blocks via

Some information helpful to understand the boot process under RT-11.
(a) In a hardware boot, the primary program in the EPROM is used
to read BLOCK ZERO on the specified disk drive media.
(b) The secondary boot program in BLOCK ZERO is usually
read into memory locations starting at address zero and normally
the first word MUST be the NOP instruction.
(c) In RT-11, the secondary boot program then reads the tertiary
boot program in blocks 2,3,4,5 of the disk drive media and those
4 blocks are sufficient to read the specified monitor and device
driver files.

Sincerely yours,

Jerome Fine
If you attempted to send a reply and the original e-mail
address has been discontinued due a high volume of junk
e-mail, then the semi-permanent e-mail address can be
obtained by replacing the four characters preceding the
'at' with the four digits of the current year.
Received on Thu Apr 04 2002 - 08:45:57 BST

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:34:29 BST