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Introduction

Running the real hardware is of course the ultimate experience with a PDP-11. However, depending on the size of the machine (and installed peripherals), your electrical bill can increase more than you would like. An other problem is the amount of heat generated.
Most of us do not have a climatized room at home, so running a PDP-11 during the summer is not possible for hours.
When you want to play with any DIGITAL Operating System available for a PDP-11, and at that same time the real hardware is not important, you have an other option.
On the Internet are several emulators available, and there are a few that emulate a PDP-11 on a Personal Computer.
So, if you have a PC :-) , install an emulator and the DEC Operating System of choice, and you have a PDP-11 on your desk .....
That is what I did, but it cannot beat the real stuff.

As a collector of PDP-11's, I also wanted to actually run the machines, and at some later time write my own software to control something with a PDP-11. The power consumption of these machines can easily warm up a big room (and it will!), so you do not want to keep them running idle for several hours while editing a source code file ...
So I started to use my PC (yuk!) to write the PDP-11 source code.
To test the code I opened a "DOS box" and started Ersatz-11 () or SIMH ().
However, I missed the 'blinkenlight' console in front of me for the real touch and feel of testing on a PDP-11.

So, I searched the Internet and found a project of Bob Armstrong www.sparetimegizmos.com to connect a real PDP-11 console with some extra hardware to Ersatz-11. However, the software in Ersatz-11 needed to control the console was not (yet?) available. See Home-made KY11 Interface for more details.

His ideas formed the base of my own project, but I wanted to design an interface that is more flexible. The result is a design to which you can connect any 'blinkenlight' console, not only any PDP-11 version with a 'blinkenlight' console, but also any other model for example the HP-1000 'blinkenlight' console!

The initial design was based on a Motorola 6802 CPU, and it still is ... there have been just minor modifications to the hardware. The "homebrew PDP-11" had its own 486DX66-based PC motherboard and a home-made console. I would never use a real console as a front-end of a simulated PDP-11. In that case I prefer the real thing! The nice thing about the selfmade console is that you can make it a lot smaller, and that led to the new design in which the old 486-based motherboard is replaced by a modern PC/104 Pentium-based board. The CMOS battery on the 486 board had developed a problem, so that was solved as well :-)
Since the PC board was a lot smaller I also bought a new smaller PC power supply.
The result is a "PDP-11/40" with a little smaller footprint then the real /40 in my computer room.


() Ersatz-11
Ersatz-11 is a PDP-11 simulator originally entirely written in assembler language by John Wilson.
Ersatz-11 runs fine in a DOS box under Windows (...) but then you loose the real-time aspect of your PDP-11 software due to the uncontrolable Windows environment. For really real-time emulation of a PDP-11 on your PC, boot the PC in MS-DOS! A free version to run in Linux is available too!
You can download the free version (with some limitions in its functionality) from
www.dbit.com.
This version is ok for hobbyist use. Commercial versions for both OS are also available.

() SIMH
SIMH is a simulator for many different classic machines. The source code is written in C and consists of a generic set of modules, and several directories each containing the modules for the specific machine implementation.
SIMH is maintained by Bob Supnik, and you can download the source files from
http://simh.trailing-edge.com.
The SIMH software also runs under DOS/Windows and Linux.