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You can run preserved PDP-1 software without owning an original machine or a replica. Choose a software simulator such as SIMH or an FPGA-based MiSTer core, find a paper-tape image, and load it using the method that matches both the image format and emulator. SIMH uses commands; MiSTer uses its on-screen display (OSD) and SD card.
Choose an emulator path
| Path | Host or hardware | How you load tapes | Best fit |
|---|---|---|---|
| SIMH PDP-1 simulator | Software simulator; consult SIMH’s current project documentation for installation and platform details. | Command line, using RIM or BLK format. | Readers who want a software-based setup and command-driven control. |
| MiSTer PDP-1 core | MiSTer FPGA system and an SD card. | Copy the image to the SD card, enable RIM mode, then select the file in the OSD. | Readers who already use MiSTer or want its FPGA-based implementation. |
| PiDP-1 software | Linux computer; the simulated front panel and peripherals can run without the physical replica. | Project-specific tape workflow, with files in its tapes/ directory. |
Readers interested in the PiDP-1 project’s virtual panel and simulated peripherals. |
| PiDP-1 replica | Optional physical replica project; its 2025 manual names Raspberry Pi Zero 2 W and Raspberry Pi 5 as board options. | Uses the PiDP-1 software and simulated peripherals alongside replica hardware. | Readers who specifically want a physical front panel, not a requirement for emulation. |
For SIMH installation, start with the Open SIMH archival software sources and current project instructions. The cited PDP-1 usage manual documents commands and configuration, but it is not a current cross-platform installation guide.
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Find a PDP-1 paper-tape image
Historic PDP-1 software is commonly preserved as paper-tape images. Open SIMH links to Bitsavers and other archival collections; the PiDP-1 manual also points readers to Bitsavers and masswerk.at for PDP-1 tapes. Search for a specific program, then read the archive’s item description and the target emulator’s instructions before loading it.
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Load a tape in SIMH
SIMH’s PDP-1 Simulator Usage manual documents a LOAD command for RIM and BLK tapes. In that manual’s conventions, the default is RIM; a .BIN filename or the -B switch selects BLK.
- Start the PDP-1 simulator and configure it for the target program. The manual documents PDP-1C and PDP-1D options, memory sizes, multiply/divide, and sequence-break controls; do not assume one configuration suits every program.
- At the SIMH command prompt, load a RIM tape with
LOAD lisp.rim. - To load RIM at the field starting at octal address
70000, the manual givesLOAD ddt.rim 70000. - For a BLK tape, use
LOAD -B macro.blk. - After loading, follow the program’s own start procedure or the instructions for its specific image. Loading a tape and starting the program are separate actions.
These commands describe SIMH’s documented interface; they are not MiSTer commands. Verify a tape’s format and the target program’s expected configuration rather than relying on its filename alone.
Load a tape in the MiSTer PDP-1 core
The MiSTer PDP1_MiSTer project page describes a core with a paper-tape reader, read-in mode, Type 30 CRT and teletype emulation, and single-step support. Its setup and tape-loading steps are distinct from SIMH’s command-line workflow.
- Install the core by copying its
.rbffile to the root of the SD card and loading it, as directed by the project page. - Copy the paper-tape image file to the SD card.
- Enable RIM mode with
F10or through theF12menu, following the core’s current instructions. - Choose the load option in the OSD and select the image. The OSD lists PDP, RIM, and BIN image-loading options; use the one appropriate to the file and core instructions.
- Once the image is loaded, use the program’s own instructions to start it. The project says Spacewar! is preloaded, so it may be available without loading another image.
Check the project page for current key mappings and menu details. Hardware multiply can be configured to reflect differences between early and later PDP-1 machines, and CRT wait behavior can be overridden. These settings may affect compatibility or display behavior, so change them only when needed for the program you are trying to run.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Use the PiDP-1 software without building the replica
The PiDP-1 Manual, 2025 Edition says its software can run on Linux with a virtual front panel; the physical replica is optional. Its software core simulates peripherals including a typewriter, Type 30 display, and paper-tape reader and punch. The manual describes GUI, web, and custom peripheral-app modes, which are specific to the PiDP-1 project rather than generic SIMH setup.
For this project, tape files are kept in the tapes/ directory. The manual lists .rim, .pt, and .bin extensions, while cautioning that extensions are not consistently applied across its collection. It recommends using the project’s tape visualizer to inspect files. The manual also outlines a historical programming workflow: ET editor to source paper tape, MACRO assembler to binary tape, and optionally DDT before loading and testing. Its quick-start material identifies preserved programs including MACRO, DDT, Lisp, and FORTRAN.
Troubleshoot image loading and startup
- Check the format, not just the suffix. SIMH’s documented default is RIM, while
.BINor-Bselects BLK in its manual. PiDP-1’s manual warns that extensions in its collection are inconsistent. Confirm the image format for the emulator you are using; do not transfer one emulator’s filename assumptions to another. - Confirm the loader interface. SIMH expects a command such as
LOAD lisp.rim; MiSTer expects an SD-card image selected through its OSD with RIM mode enabled as directed by the core. Mixing these procedures will not work. - Check the program’s hardware expectations. In SIMH, review the manual’s CPU and memory configuration choices for the target software. In MiSTer, hardware multiply and CRT wait behavior are configurable and may matter for compatibility or display.
- Distinguish loading from starting. A successful tape load does not necessarily launch the program. Follow the program’s own start instructions or its emulator-specific documentation.
- Inspect uncertain PiDP-1 tapes. Use the tape visualizer identified in the PiDP-1 manual rather than inferring format from an extension alone.
Why paper-tape images are central to PDP-1 software
The Computer History Museum explains that most PDP-1 software was released on paper tape and that the museum copied original tapes to protect them. Its restoration account describes a progression from toggling a short bootstrap loader through switches to using paper-tape programs and DEC diagnostics. These historical steps help explain why modern emulators load tape images rather than ordinary contemporary installers.
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