PDP-8 notes: Dumprest and paper-tape diagnostics

These are my rough notes about using paper-tape diagnostics and dumprest on the PDP-8.

This page focuses in particular on using dumprest on a Windows machine in a Cygwin environment.

I have a separate page here that provides some tips for setting up Cygwin.

Dumprest

Dumprest is a series of utilities by David Gesswein that allow image transfers between a physical device on a real PDP-8, and a PC. The “dump” utilities send an image from the PDP-8 to the PC, and the “restore” utilities do the opposite. They are device-specific, so you need to run the pair that corresponds to the specific device and operation.

The dumprest package is distributed as a ZIP file. There is one ZIP file for UNIX-like systems (“dumprest.zip”), and one for use on Windows systems which contains Windows binaries built using cygwin (“dumprest_cygwin.zip”).

Dumprest (which also contains companion utility sendtape) can be found on David’s site here -> https://www.pdp8online.com/ftp/software/dumprest/. Sendtape is used to transmit a BIN format papertape image from a PC to the PDP-8 over the console cable. The BIN file can be the PDP-8 component of the relevant dumprest utility, or a paper-tape diagnostic.

There is a very good “readme file” included with the dumprest package. A local copy of the readme file is available here. There are also detailed instructions (such as the run address) in the relevant dumprest assembler file.

Once you download and unzip the dumprest package, you might also want to download a copy of the PDP-8 BIN loader paper tape and store it in the same directory, as you’ll need to use it to transfer the PDP-8 component of the dumprest program (the “.bin” file) from the PC (which will be running sendtape) to the PDP-8 (which will be running the BIN loader).

Here is the process for running dumprk05 on a Windows 11 machine (with all PC commands entered through the cygwin environment) and a PDP-8/e, once the downloading steps described above have been done:

  • In cygwin, change from your cygwin home directory to the dumprest directory. For me that was done using the command “cd /cygdrive/c/cygwin-files/dumprest/dumprest”. If needed, you can see the mounted directories in cygwin by typing the “mount” command”. Check that you can see the dumprest files there using the “ls -l” command
  • Use the command “ls /dev/tty*” to identify your RS232 interface
  • Edit the file “dumprest.cfg” using “vim” to set the serial line parameters. On the second line, use “0” for 1 stop bit, or “1” for 2 stop bits (we used “1”). Update the third line to specify the name of your serial port. Use “:wq” to save and exit
  • Toggle in the RIM loader on the PDP-8/e and run it at address 7756
  • Run sendtape on the PC to send the BIN loader papertape (I used “dec-08-lbaa-pm_5-10-67.bin”) to the PDP-8
  • Run the BIN loader at 7777
  • Run sendtape on the PC to send dumprk05.bin to the PDP-8
  • Start dunprk05.exe on the PC, and then start dumprk05.bin on the PDP-8 at starting address 0200
  • Blocks will now transfer over the serial cable to the PC and you will see an update (new cylinder number) on completion of each cylinder

My first attempt at using dumprk05 was on 31.08.2025. I was attempting to dump my cartridge labelled “#7 DECUS” from a real RK05 to my 8/F over a KL8E interface at 9600 baud, 1 stop bit. The transfer went ok, apart from the bad block mentioned below, and took about 40 minutes.

Here’s the dialogue:

malco@x1-carbon /cygdrive/c/cygwin-files/dumprest/dumprest
$ ./dumprk05.exe
Enter file name to receive
decus.rk05
Cyl 75
sector 2410, cyl 75 side 0 sect 10 bad
Cyl 203
Done

The resulting file (decus.rk05) is 3,424KB and I’ve not been able to open it in SIMH. Not sure what the problem is yet. The disk image can be downloaded from this link.

A directory of that disk (as well as a list of the “.BN” files on the “A side”) can he accessed here. This was taken from the real disk, not from the image.

Diagnostics

Sendtape can also be used to send a paper-tape diagnostic to the PDP-8.

The process is as follows:

  • Key in the RIM boot loader on the PDP-8
  • Load the BIN loader, by running the RIM loader on the PDP-8 and sendtape on the PC
  • Load the diagnostic, by running the BIN loader on the PDP-8 and sendtape on the PC

Paper-tape diagnostics need to be in BIN format. This is what is produced by the PAL8 assembler. If you don’t have a BIN (paper tape) image to use, you can take a SV or DG format diagnostic from an OS/8 distribution, and use Vince’s “svtobin” utility to convert it to BIN format.

Useful places to find diagnostics

  • The website for the PDP-8/e emulator for the Mac
  • deramp.com (use this link to access them)
  • Bitsavers?
  • Vince’s website?
  • PiDP-8 website?
  • Don North’s website (use this link to access them)

Other useful information

The PDP-8 paper-tape manual has information about the different paper-tape formats.