PDP-11 Diagnostics - Introduction

Parent Category: Tools Category: PDP-11 Diagnostic Database Written by Administrator

Digital Equipment Corporation (DEC) made diagnostic programs for every PDP-11 component they ever made  (of course also for other computers lines, as PDP-8 and VAX ... here we focus only PDP-11's).

0167 CZQAGJ0 PDP11diagModuleIdx.pdf

The database

Over several months I collected all diagnostic files I could find. Most are already on bitsavers.

In daily work  you need to answer questions like "What diagnostics are there for device xxxx?", "Where can I find executables for diagnostic module yyyy?",  "Did I read all available documentation for module zzzz?", and so on.

When I observed how much time I spend navigating through the existing documents, the time to build up this database seemed well invested.


The DEC diagnostics are well documented, but access is difficult: Many documents are old high-peed printer printouts, which have been micro filmed, and scanned again. So readability is poor. And the interesting "user guide" chapters are often burried between 100+ pages of some cross-references or assembler listings.

In many cases I spilt off big manuals into separated PDF pages and linked every manual page with the related diagnostic module.

A good start to read is chapter 2 in the PDP11/23 User manual. Then explore the files assigned to _MAINDEC_DOC, _MPG_DOC, _X11_DOC and _XXDP_DOC.

MAINDEC-11-DZQAB-B-D MAINDEC User Reference Manual Oct73.pdf

Types of diagnostics

There are far far more different diagnostics than there are devices to test. These factors cause multiple diagnostic variants:

Target platform

A diagnostic will not only test a specfic device, it also has to run on a specfic PDP-11 system just as a regular program.

So there are variants for different PDP-11 system, depending on CPU types, and memory size. Some devices can also be tested for different platforms: disk and tape drives can be connected to PDP-8's or VAXes, and then there are diagnostics for these platforms too.

Run time environment

Diagnostics come in different formats, depending on the environment they run in.
The same diagnostic may appear as

Level of test



DEC delivered diagnostic programs always in whole "media packages". A package is the set of diagnostices on a common medium needed for a specific machine,.

Packages were packed according to

A media package includes many file types:

A single diagnostic can be very simple (example: CKBKA0 tests only the MUL instruction of a 11/40), or very comprehensive (OKDDD0 tests the whole 11/53 CPU board with processor, RAM, serial lines units, clock and bus arbitration).

The "XXDP" distribution allows to generate media packages for differnet platforms.


PDP-11 diagnostics were produced and used over the whole PDP-11 life span, at least from 1969 to 1992. Over time, the format of the diagnostics changed. I know of these: