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We began work on the IBM 1130 emulator in the fall of 2001, with little hope of ever having a copy of the original operating system to run on it. In March 2002, Douglas Jones sent us copies of the IBM build listings on microfiche. It seemed like a long shot to scan and OCR them, but we began to experiment with the concept. We also knew that there was a binary "system load" card deck in Milpitas, CA, part of the Computer History Association of California (CHAC) collection, but getting a working card reader to load it in was going to be difficult. Then, in April, 2002, we received a letter through the IBM1130.org guestbook from Oscar E. Wyss in Switzerland who indicated that he just happened to have the entire source code for DMS on his website, available for download. (Oscar emailed the next day, "Thank you for your interest and for filling my access log.") Little real work got done over the next couple of weeks, and our cross assembler got a workout. DMS is loaded onto a blank disk cartridge through a "system load" procedure. Starting with a single bootstrap card that is followed by a succession of loader programs and system object modules, about two drawers of binary punched cards must be read in to populate the disk. The trick was not only to assemble the system components, but to correctly construct the load deck. The initial portion of the load deck, illustrated above, is composed of four components:
This is followed by text configuration cards, the System Load
program Part 2 and the system programs in relocatable format, and
finally the library routines interspersed with
Source code readings filled in the missing pieces. There was quite a bit of trial and error involved. Three whole days were lost to a single oversight in reading the documentation: an A or F punched on a certain configuration card mean that the Assembler or Fortran are not to be loaded, while a C punch indicates that Cobol is to be loaded. (You'd think they'd be consistent, wouldn't you? Noooooo.) Without the correct punches, the load process halted. Finally, on the morning of April 23, 2002, DMS booted up and printed the cold-start job banner we last saw 25 years ago. This is a copy of that first printout: Who Would Have Guessed?It turns out that DMS could never have been built on the 1130 itself. First, the 1130's macro assembler does not support the crucial SBRK output directive needed to separate the system overlay modules. More surprisingly, there are bugs in the assembler that prevent proper compilation of the interrupt handlers and trigonometric library routines! For example, consider this source code line from module R2FSIN.ASM (single-precision sin function): This is a fixed point real constant. The generated code from the original IBM cross assembler is:
while the output from the IBM 1130 macro assembler is:
Granted, that's an error of only 1 part in 213, but still... yikes! We believe that IBM built its DMS distributions with a cross assembler on the System /360 or /370, and the fiche listings were generated by that mechanism. Preserving Historic SoftwareOur experience in resurrecting DMS showed us that an historic operating system can indeed be brought back to life. We believe that the experience of using an historic system adds much to one's ability to appreciate its technical and historic significance. It also provides a concrete motivation to preserve not only hardware and software, but also the body of knowledge and experience necessary to support and operate them, much of which never made it to written form. We also learned several lessons:
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