A working PDP-1

The most ambitious restoration is also the most literal. The Computer History Museum in Mountain View returned one of its original PDP-1 machines to working order, with the restoration completed in October 2005. The team, Lyle Bickley, Joe Fredrick, Bob Lash, Rafael Skodlar and R. Tim Coslet, debugged the hardware bit by bit, sourced spare parts, and brought the paper-tape reader, console and Type 30 display back to life. Spacewar! is once again played on this machine in regular public demonstrations, sometimes with original authors and players present: Steve Russell, Alan Kotok and Martin "Shag" Graetz have all played it again on the restored hardware, and Peter Samson and Dan Edwards have been photographed at the Type 30 display. It is as close as exists to playing the 1962 game as it was meant to be played.

The museum also recovered and documented the game's source. Its 4.1 listing, reconstructed during the restoration, is among the cleanest surviving texts of the late MIT game, and several of the source files used elsewhere on this site descend from that work. The museum's full account is published at computerhistory.org/pdp-1.

A PDP-11 brought back from a printout

The 1974 PDP-11 port by Larry Bryant and Bill Seiler had been lost when DECUS discarded its source materials. Mattis Lind recovered it from a printout Seiler had kept, transcribing the listing by OCR and hand, reassembling it with the period PAL-11S assembler, and adapting the I/O to a single-board AR11 converter so it would drive an X-Y oscilloscope with hand-built joysticks. This is restoration as textual scholarship as much as electronics: a forty-year-old listing collated byte-for-byte and made to run again.

We give this version its own page, because it sits across the line between a port and a restoration: Spacewar on the PDP-11: Bryant, Seiler and the GT40 ›

The PDP-1 in programmable logic

Where the museum repairs the original, the MiSTer project rebuilds it. The PDP1_MiSTer core implements a complete PDP-1, instruction set and 4 kB of core memory, in an FPGA on a Terasic DE10-Nano board. It runs the canonical software directly: Spacewar! (versions 2B and 4.1), the Minskytron, the Snowflake demo, the Expensive Desk Calculator and DDT. The hardest part is the screen: the original Type 30 CRT, with its 1024×1024 addressing and its slow, persistent phosphor, is recreated with shift registers, row buffers and a blur circuit so that the decay and afterglow look right on a modern display. The author credits Norbert Landsteiner for guidance, and notes that Ben Gurley "designed PDP-1 in 3 months". Hackaday covered it in December 2018; the core is on GitHub.

A replica you can switch on

The PiDP-1 takes the rebuild in the opposite direction from the FPGA core: rather than the logic, it recreates the console. Made by Obsolescence Guaranteed (Oscar Vermeulen, after his earlier PiDP-8 and PiDP-11 replicas), it is a historically accurate reproduction of the PDP-1's front panel, its banks of switches and lights, driven by a Raspberry Pi running Angelo Papenhoff's PDP-1 simulator underneath. It comes as a kit or assembled, in console and rack variants, and even reproduces DEC's own indecision over the cabinet colour with interchangeable white and blue panels. It runs the full software canon, Spacewar!, the Minskytron, Munching Squares, the Snowflake, the assembler and debugger, so that the first video game runs on something you can stand in front of and toggle by hand, the bodily experience the emulators cannot give back. It rests on the same two foundations as much of this page: Papenhoff's simulator and the Computer History Museum's restoration.

Emulation as restoration

The most widely played restoration runs in a web browser. Norbert Landsteiner's masswerk.at/spacewar is a virtual PDP-1 emulated in HTML5/JavaScript, running the original code with "special attention ... on accurate timing and on a recreation of the appearance and the unique experience of the original CRT display", down to the Type 30's dual-layer phosphor. It loads authentic paper-tape images, including a 3.1 binary dated "24 sep 62" from Steve Russell's archives, and is accompanied by an extensive body of documentation, Inside Spacewar!: A Software Archaeological Approach to the First Video Game, source listings, disassemblies and reconstructions. It is the emulator behind the Play page here, and a major scholarly resource in its own right.

The whole machine, in a browser tab

The Internet Archive runs Spacewar! in the browser on an emulated PDP-1, using the MAME/MESS PDP-1 driver compiled to JavaScript as JSMESS. It plays the original 1961 code from a .RIM paper-tape image, and rather than show only the screen it reproduces a whole console on one canvas: the round Type 30 CRT in the upper-left, the typewriter output along the bottom, and the banks of switches and lights at the upper right (the "Control Panel" is reached, as on the machine, by holding the left CONTROL key). It is a different restoration choice from Landsteiner's, less a recreation of the experience than a working exhibit of the entire machine, assembled by the MAME/MESS and JSMESS teams. The emulator itself is MAME.

Reading the 1962 code, technique by technique

Some restoration is textual rather than electronic. In 2011 the MIT GAMBIT Game Lab, in a "digital archaeology" project led by Owen Macindoe, set out to replicate Spacewar! by reading its original PDP-1 source closely, learning Macro assembly from the 1962 manuals to do so. They worked through the unfamiliar idioms of the period, octal by default, bitwise tricks, indirect addressing and hand-managed memory, documented the programming techniques the original used, and re-implemented the game (down to an Arduino demonstration version). It is the same move this project makes: to treat the listing itself as the object, and reading it as a form of recovery. Source: GAMBIT, "Digital Archaeology: Investigating Spacewar!" (2011).

Replicas, lasers and write-ups

Spacewar! restoration shades off into a wider culture of recreation and homage. Hackaday's Spacewar tag collects projects from across this scene, including a galvanometer-driven laser vector display built from recycled 3D-printer parts (2016) and an overview of the PDP-1 as "the machine that started hacker culture" (2017), alongside the FPGA and PDP-11 work above. These are not scholarly editions, but they are part of the same impulse: to make the first video game move again on something you can stand in front of.

Restoration as interpretation

For a Critical Code Studies project, restoration is not merely background. Every one of these efforts is a reading of the code, and each leaves a trace. The museum's repair decides which machine counts as "the" PDP-1; Lind's transcription resolves ambiguities in a scanned listing; the FPGA core makes explicit, in logic, assumptions the original left implicit; the emulator chooses how the phosphor should fade. The runnable artefact we examine in 2026 is always the product of such choices. Reading the code means reading the restorations too.

← The versions and the ports table   Timeline →

References

• Computer History Museum, PDP-1 Restoration Project (restoration completed October 2005; team and Spacewar! demonstrations).
• Mattis Lind, SPACEWAR (PDP-11 recovery, 2021), and Hackaday's write-up. See also our PDP-11 page.
• PDP1_MiSTer FPGA core, and Hackaday, December 2018.
• Obsolescence Guaranteed (Oscar Vermeulen), PiDP-1 replica-panel kit, running Angelo Papenhoff's PDP-1 simulator.
• Norbert Landsteiner, Spacewar! emulation and documentation, masswerk.at.
• Hackaday, Spacewar tag, for the wider recreation scene.