Emulating RT-11 in SIMH

I was asked if I could write some instructions describing how to get RT-11 to boot in an emulator, so here goes...

To boot a PDP-11 in the SIMH emulator (on Windows), the first thing you need is a copy of the SIMH program.  You can get that from here: http://simh.trailing-edge.com/sources/simhv38-1-exe.zip

From that zip file we're interested in the application called "pdp11.exe", you should easily find it inside the root of the zip file.  Extract pdp11.exe to a folder on your PC - this is the SIMH emulation of a PDP-11.  It won't do anything interesting yet though.

The next thing that you need is some software to run on the emulator, I've been using the RT-11 OS and you can download that here: http://simh.trailing-edge.com/kits/rtv53swre.tar.Z

That is a compressed set of RT-11 files, including a disk image.  Inside, there should be a /Disks folder containing the disk image called "rtv53_rl.dsk".  Save that dsk file to the same folder where you saved pdp11.exe.

Now we need to tell SIMH to boot, and to do that we create an ini file and save it into the same folder as pdp11.exe.  You can do that in notepad.  The ini file should have this content:

set rl enable
set cpu 512k
set cpu 11/53
attach rl0 rtv53_rl.dsk
boot rl0

Save that content as "pdp11.ini" in the same folder as everything else.  It will tell SIMH to emulate a PDP-11/53 with 512k or RAM, and boot from the disk image.

Now you should be able to run pdp11.exe and it should boot from the disk and start running a brand new copy of RT-11.  You're on your way...

Make a disk bootable in RT-11

In the end it was very easy to get my winchester drive to be bootable.  I just had to read the manual really...  This was what I used:

copy/boot dk0:rt11xm.sys dk0:

The trick is to already have a copy of the boot-file (RT11XM.SYS in my case) on the disk.  The "copy/boot" command then just moves the file from one part of the disk, to the boot section.  Easy.

I used that to make my Winchester Drive bootable, so now I'm booting straight from the fixed disk.

Making an RT-11 v5.3 disk image

I realised that if I could get a floppy disk that booted into RT-11 v5.3, then I might be able to add the DECUS C compiler and have a boot disk and C compiler. This is the procedure I used to make my first RT-11 v5.3 boot disk.

Using SIMH, boot into RT-11 v5.3, making sure that you have blank RX33 disk image attached as DK1:. Then use these RT-11 commands to copy the files to the floppy disk image:

COPY/SYS SY:*.SYS DK1:*.SYS
COPY SY:VBGEXE.SAV DK1:
COPY SY:DIR.SAV DK1:
COPY SY:BUP.SAV DK1:
COPY SY:DUP.SAV DK1:
COPY SY:IND.SAV DK1:
COPY SY:LINK.SAV DK1:
COPY SY:KEX.SAV DK1:
COPY SY:PIP.SAV DK1:
COPY SY:V5USER.TXT DK1:
COPY SY:STARTX.COM DK1:
COPY SY:UCL.* DK1:
CLOSE

Then, shut down SIMH. We'll next use PUTR to make the RX33 disk image bootable (this assumes that you have called the image rx33.dsk and that it is in the same folder as PUTR):

MOUNT a: rx33.dsk /rx33 /rt11
BOOT a:
     RT11XM
     DUX
DISMOUNT a:

That's it. The RX33 image should now be bootable. Try it out in SIMH to make sure.