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Burroughs B5500 Mark XIII System Software


The Burroughs B5000 and B5500 were perhaps the first computer systems designed with the idea that they would require a significant operating system in order to run. Operating systems in the early 1960s were known as control programs. The designers at Burroughs envisioned a program that would automatically administer the entire system's operation, and thus created what became known as the Master Control Program, or MCP. You can read the story of how this came about in the 1985 B5000 oral history transcription.

As a result of that design approach more than 50 years ago, having a B5500 emulator today is not all that interesting unless you also have the associated system software to make it do something. Alas, software was maintained in those days on punched cards and 7-track, open-reel magnetic tape, neither of which have seen much use in the last 30 years. Open-reel magnetic tape, in particular, is not known for having long-term archival qualities.

Fortunately for us, Sid McHarg of Seattle, Washington (US) had preserved a set Burroughs 7-track release tapes for the B5500 Mark XIII (October 1971) version of the system software. Even more fortunately, Sid was able to work with Paul Pierce of Portland, Oregon (US) to recover the data from those tapes. We are indebted to Sid and Paul for their work on those tapes and making the resulting data available.

Burroughs became part of Unisys Corporation in 1986. Unisys still owns and holds copyrights on the B5500 system software, so Sid worked with Bob Supnik, then VP of Engineering and Supply Chain at Unisys, to arrange an educational/hobbyist license for this software. We have acquired such a license, and are thus indebted to Bob and Unisys for generously allowing us to use the B5500 Mark XIII software under the terms of that license.

Downloading the Tape Images and Source Files

Our license with Unisys allows us to make the Mark XIII software available to others under the terms of that license. There are three tape images and a ZIP archive of decoded ASCII source, as enumerated below. To download one of the files, please click its corresponding link. The resulting page will display the applicable terms of the Unisys license, and for the tape image files, a directory of the files on that image. Confirm your acceptance of the license terms to begin the download. You will need to download at least the SYSTEM image in order to run the emulator.

SYSTEM image (2.6MiB .zip) contains object code for the release, including the Datacom MCP, Timesharing MCP, System Intrinsics, CANDE timesharing system, compilers, and utility programs. It also contains source files for a few utilities, and a set of source-level patch files for the release.
SYMBOL1 image (2.2MiB .zip) contains the source code for the Datacom MCP, System Intrinsics, and compilers.
SYMBOL2 image (2.1MiB .zip) contains the remaining source code for the release, including the Timesharing MCP, CANDE, and utility programs.
Release ZIP archive file (5.2MiB .zip) contains the source and object code for the entire XIII release, translated from 6-bit B5500 internal code to ASCII text files, using the standard retro-b5500 substitutions for the B5500 characters that do not have ASCII equivalents.

Format of the Tape Image Files

Each of the tape images above is a standard ZIP archive file containing a single ".bcd" file. That file is a binary octet stream, i.e., a blob of 8-bit bytes. Each octet represents one data frame (6-bit character) from the 7-track tape. The low-order six bits of each octet contain the binary data from the tape frame. The next-higher bit is the odd-parity bit. The high-order bit in the octet will be a 1 if that frame is the first one in a physical tape block, and 0 otherwise. A tape mark (EOF) is represented by a block containing a single octet with the hexadecimal code 8F.

The files on the tape image are formatted in B5500 "Library/Maintenance" format, which is described in the B5500 MCP Reference Manual, 1042462 (June 1969), page 8-1. Tape label records are described in Appendix B of that reference. The format of disk file headers is described in the B5500 Operation Manual, 1024916 (September 1968, revised June 1971, PCN 015), page 5-41. B5500 character codes are described in Appendix A of that reference.

We have developed a few HTML/Javascript utilities to read these tape images and decode their data. See B5500LibMaintDir.html, B5500LibMaintDecoder.html, and B5500LibMaintExtract.html in the /tools directory.


Copyright (c) 2013, Nigel Williams and Paul Kimpel • Licensed under the MIT License
Revised 2017-05-28