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28 Dec 2004

mxload - Read Multics Backup Tapes

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Olin Sibert

In the waning days of the Multics product, Jim Homan and Olin Sibert created the mxload package for reading Multics backup tapes.

The software can read standard-format tapes, reload data, produce maps, unpack archives, Forum meetings, message segments, and mailboxes. It can operate from the command line or be driven by a control file. It can read tapes directly (at least on Unix systems), but in these days, it's probably easiest to read the tape into a file and run mxload or mxmap on the file instead.

Segments that contain only 8-bit ASCII are, by default, converted to 8-bit format when reloaded with (mxload). Segments that have high bits set in any byte, or that are in one of the recognized formats (mailbox, forum meeting, etc.) are reloaded in a packed 9-bit format that can be processed with one of the other commands (mxarc, mxascii, mxmbx, or mxforum).

On the off chance that there are still people who want to read Multics tapes (or tape data), we are making the mxload package generally available on this website. You can download Windows binaries and documentation here,

If you're more adventurous, you can also download the sources here. It builds without incident on Windows 2000/XP. It was originally built for SunOS Unix, and worked fine on many similar systems, but we haven't tried building it for Linux.

If you do have tapes, please be careful reading them. Modern streaming tape drives can easily ruin an old 9-track tape if there is any stickiness or other crud on the tape. Contact Olin Sibert if you would like any assistance or advice.

About the Software

The mxload package consists of the following programs. Click on the program's name for the Unix-style manual page documentation.

A paper from a 1988 HLSUA (Honeywell Large System User's Association) meeting where the product was introduced is here (7-page PDF), and the slides are here (15-page PDF).

The full user's manual is here (21-page PDF).

mxload Main program: reads a Multics tape (or tape file) in backup_dump format and extracts files and directories as requested.
mxmap Prints out a map of the tape's contents. Good for exploring a tape and verifying its content.
mxascii Converts a file form 9-bit format to 8-bit format, stripping the high bit.
mxarc Extracts files from Multics-format .archive segments.
mxmbx Extracts mail messages from Multics-format .mbx segments. Several conversion options, including one file per message and Unix-style mail files.
mxforum Extracts postings from Multics Forum meetings (.forum MSFs). Several conversion options, as for mailboxes. Sorry, no support for continuum :-)

This software hasn't been touched since 1993 or so, although the Windows binaries were built just this year and seem to work fine.