PDP-11 Live CD running Zork

  Live CD image with Zork

By popular demand, here is a PDP-11 Live CD that is configured to auto-run the 'Dungeon' game (aka Zork) in a PDP-11 emulator.  Well OK, when I say 'popular demand' I mean that a colleague of mine mentioned it in idle conversation...

I got the game files from here: http://www.dbit.com/pub/pdp11/rt11/games/

And if you don't know about the historic computer game of Zork, I suggest you have a read on wikipedia: http://en.wikipedia.org/wiki/Zork.

Improved PDP-11 Live CD

  Live CD image

The previous PDP-11 Live CD that I made is great, but it only works with IDE CD-ROM drives, so you cannot use it if you have a SATA or USB CD-ROM.  Which is a shame.  So I wanted to make a version that doesn't rely on having CD-ROM drivers for DOS, since it's unlikely that I'd be able to support all of the different types of drive.  I have tried to get my external USB CD-ROM drive to work under DR-DOS and found that I couldn't make it go.

So, for a few days I have been struggling to create an "El Torito" hard disk image, so that I could make a CD bootable version of a hard disk.  I haven't gotten it to work yet.  I even tried this (twice actually) by taking the HxD hex editor to an ISO file.  I've given up for the time being, but I'll probably come back to it.

However, I can get floppy disk "El Torito" images to work perfectly, including the 2.88 Mb variety.  That's how I got the previous Live CD to start (but I was only using a 1.44 Mb image that time).  So with a bit of lateral thinking I realised that my PDP-11 disk compresses quite well.  So I went off an got an UNZIP program for DOS, from here ... or to be specific, I downloaded unz600x3.exe from: ftp://ftp.info-zip.org/pub/infozip/msdos/.

This means that I can fit DR-DOS into a 2.88 Mb floppy image along with a compressed copy of the PDP-11 emulator and disk.  Since everything is inside the 2.88 Mb image, we don't need to load CD-ROM drivers in DOS.  It means that this bootable ISO will work with SATA and USB CD-ROM drives, it doesn't need the drivers since it's all done by the BIOS and the magic of El Torito.  Cool.

PDP-11: RT-11 Live CD with Basic-11

  Live CD image

[NOTE: I have since made a better version here.]

This ISO image of a bootable CD is the combination of two different threads I have been working on: how to make bootable CDs and how to set up RT-11 with Basic in SIMH, the PDP-11 emulator.  This CD only works if you have an IDE CD-DROM drive though.

So I took the bootable CD image that I had already made and added SIMH for MS-DOS.  Then I added my RT-11 / Basic-11 disk image.  I set SIMH to start up automatically from a 16Mb RAM disk.  It all seems to work. It is pretty fast in comparison to a real PDP-11!  Because it is running from a DOS RAM disk, you get read/write access under RT-11 (until you switch the power off).  But it does mean that you can't mess it up since you get a clean install each time you boot the CD. Oh, and if you're looking for a manual on Basic-11 I've posted some stuff here.

So... if you'd like to have a play with an ancient operating system, give it a try.  Burn the ISO to a CD or boot it directly in Virtual PC or VirtualBox.  I've tried it with as little as 32Mb RAM, and it works fine. When I get time, perhaps I'll do an ancient Unix Live CD as well.

PDP-11 on DR-DOS/OpenDOS

I have been busy trying to get the Ersatz-11 emulator to run on DR-DOS, which seems to work OK (more about that another time).  Then I decided to try getting the whole thing to boot from CD.  This would give me a PDP-11 Live CD.  Anyway, whilst having a rummage round in my pile of old junk hardware I found a motherboard given to me by my friend James.  It has 32Mb RAM on board and a 200MHz AMD K6 processor.  I don't have any IDE hard disks, but I do have an old CD drive.  So I started wondering if I could turn this lot into a PDP-11.  This is the machine on the bench:

AMD K6 motherboard

So the next thing to do was to see if it boots, so I tried a linux CD I had lying around:

Booting linux on the AMD K6

...which works a charm.  So the next thing was to try my PDP-11 live CD.  Guess what?  It only works:

PDP-11 live CD in action

This is sooo cool.  You can see I'm running my ASCII mandelbrot program in celebration.  In fact, this is so cool that I've gone and bought a brand new Intel D410PT motherboard and I intend to rig it to run as a PDP-11.  I expect that will fly.  I will use a solid state disk and have old software running on new hardware.  In the meantime this AMD K6 based prototype easily outperforms my real PDP-11/53.