I just received an email from my chum Alvin in the UK. The subject line of this message was: “I can see you dribbling from here!” I’m assuming he was talking metaphorically about my predicted actions upon reading the contents of his email, but we can’t rule out the possibility that he was actually watching me via my webcam (the years have not been kind).

The gist of Alvin’s communication was to point me to a PDP-11/70 Replica Kit called the PiDP-11 (because it’s based on a Raspberry Pi).

OMG, this takes me back. The PDP-11 (Programmed Data Processor-11) is one of the most famous machines in computing history. A series of these little beauties was manufactured by Digital Equipment Corporation (DEC) from the early 1970s through the mid-1990s.

The first model, which was named PDP-11/20, was shipped in the spring of 1970 with a price-tag of 20,000 USD. The 16-bit CPU had six 16-bit general-purpose registers, a program counter, and a stack pointer. The primary memory was a maximum of 56 Kbytes (28 Kwords) implemented as a magnetic core store. Input and output were typically performed via a paper tape reader/writer.

My second position after graduating university was circa 1981 at a small startup called Cirrus Designs. The main (well, only) computer when I joined was a 16-bit PDP 11/23 minicomputer, which DEC introduced in 1979. We each had a terminal and keyboard connected to this machine, which was barely able to support six people each using a line editor (or one person using a screen editor).

In addition to the cabinet holding the central processing unit (CPU), we had a hard disk drive in a second enclosure that was about the size of a washing machine. The disk itself was a multi-platter affair that looked a bit like a wedding cake when seen under the glass dome that was employed when taking it out. The remainder of the cabinet was devoted to power supplies and the disk controller.

Despite its physical size, this disk could hold only 1 megabyte of data. Also, there was only one partition (what we would call a folder today) containing everyone’s files. The system used the classic 8.3 file naming convention, so any files that started with the letter ‘M’ belonged to your humble narrator.

I could tell you some tales, but we digress… Introduced in 1975, the 11/70 was arguably the largest PDP created by the elves at DEC. Isn’t it amazing that Oscar Vermeulen of Obsolescence Guaranteed has been able to replicate this functionality in his PiDP-11 using a Raspberry Pi as the computing engine. Take a look at this video to see this little rascal in action (the PiDP-11, not Oscar).


Costing $270, this 6:10 scale replica is beautiful to behold. Observe the key required to turn the machine on (I’m definitely going to add this feature to one or more of my future projects). As Oscar says:

This is a professionally made, no-compromise PiDP-11. Injection molded case, exact replica switches and whatnot […] You could look at this as a smallish PDP-11/70, built with modern parts. Or alternatively, and equally valid, as a fancy front panel case for a Raspberry Pi.

Looking at the PiDP-11 really takes me back in time. Back at Cirrus Designs, when we first turned our PDP-11/23 on, we had to use the switches on the front panel to enter the instructions that formed the lowest-level bootloader. All I can say is that I love the blinking lights and I feel an incredibly strong urge to play with its switches. Thinking about it, I’d really like to build one of these bodacious beauties and then use it as the main interface to control something at home or in my office. How about you? Could you be tempted to invest in one of these kits?