Making an RT-11 boot disk

Philipp Hachtmann hachti at
Tue Apr 10 19:33:07 CDT 2007

Ethan Dicks wrote:
> On 4/10/07, David Betz <dbetz at> wrote:
>> Thanks again! I have now successfully installed a minimal RT-11 on
>> the RD54 of my PDP-11/73 system and it boots! Now I just have to
>> configure it with the programs I need (like DECUS C).
> Well done.
>> I guess RT-11 uses 512 byte blocks. My RD54 says it holds around 64k
>> blocks. That's about 32mb.
> That's the first partition.
>> What happened to the rest of the 150mb RD54?
> It's still there, lurking.
>> Is it possible to put more than one partition on the drive or
>> to convince RT-11 to use more than 32mb of the disk?
> RT-11 uses, IIRC, 16-bit block pointers... 65536 x 512 bytes == 32MB,
> the largest swath of a big drive it can grab in one chunk.  I've never
> personally run RT-11 with a disk over 32MB, so I don't know how it's
> done, but I know it can be done.  It might or might not depend on what
> version of RT-11 you have.  I *think* if you have MSCP support, you
> always have the ability to have multiple partitions on your large
> drives, but someone with experience on new(ish) hardware should chime
> in.  The largest machine I ever ran at home was an 11/23 with a couple
> of RL drives.  When I did use RT-11 on an 11/73 with a large disk, it
> was under TSX-11, and without the docs in front of me, I'd hesitate to
> quote technique from memory.
> You should be able to find what you are looking for in the RT-11 docs
> for versions of RT-11 > 5.4, at least.  Dunno about < 5.4.
> -ethan

It is possible... I use an Emulex SCSI controller on my 11/23+ and it 
works with multiple partition support via MSCP.
Each DU: driver can control several partitions (7?). It has to be 
configured... Don't know how I did it. But I *think* there was something 
about a "set" command.
The partitions on the drives (HDDs, CDROMs, ZIP) are sequential 32MB 
blocks. Cool to use with SIMH images: "dd-compatible" :-)
The manual (?) mentioned the possibility to duplicate the DU: drivers 
(i.e. copy du.sys to xx.sys etc.) in order to support more partitions. 
But I had bad luck with that. The other issue was that I was not able to 
boot from one another drive than DU0:

Good luck! If you have trouble, I can dig into the few runnable images I 

Philipp :-)

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