Altair ROM BASIC

[deramp5113]

I just realized today that the only copy I've ever seen of the ROMs from the Altair 88-RBM board have at least one modification versus the original ROMs. Does anyone still have this board that could dump the ROMs for me? I want to see what other differences - if any - there may be.

The difference I noticed is that the copyright phrase (Altair ROM BASIC Ver 4.1 Copyright 1977 by MITS Inc.) has been disabled in my copy by changing the leading "A" to a zero which prevents the string from displaying. Of course, that's easy to restore, but I'm curious if other mods have been made. For example, I've noticed in the past that the disk boot loader code is present in the BASIC ROMs at FF00-FFFF. Now I'm curious if that was original or added by the same person who disabled the copyright string.

Mike D

 

[labomb]

I just realized today that the only copy I've ever seen of the ROMs from the Altair 88-RBM board have at least one modification versus the original ROMs. Does anyone still have this board that could dump the ROMs for me? I want to see what other differences - if any - there may be.

The difference I noticed is that the copyright phrase (Altair ROM BASIC Ver 4.1 Copyright 1977 by MITS Inc.) has been disabled in my copy by changing the leading "A" to a zero which prevents the string from displaying. Of course, that's easy to restore, but I'm curious if other mods have been made. For example, I've noticed in the past that the disk boot loader code is present in the BASIC ROMs at FF00-FFFF. Now I'm curious if that was original or added by the same person who disabled the copyright string.

Mike D

Hmmm... you've peeked my curiosity. I located a dump of the ROMS that I found online way back in 2013, and it does indeed have a 0 byte where the 'A' should be, as well as the boot code at $FF00.

I also located a dump (not really a dump actually, but rather a terminal emulator capture of the ROM contents... in decimal no less!) that I believe I did even further back in 2004. It too, has the 0 byte and the boot code tacked on to the end.

Nothing definitive here, and I can't imagine why, but perhaps the copyright was indeed disabled by MITs. I cant find a document/addendum that is specific to the ROM variation of BASIC... but I would think there would be mention of the disk boot capability.

 

[deramp5113]

Martin Eberhard dumped the ROMs from two of these boards that he has: an 88-RBM and an 88-RBM II. The ROMs on the two boards had similar date codes. The content of both sets of ROMs was identical and the Altair banner and copyright were suppressed in both sets. We surmise that Pertec themselves suppressed the Altair banner because it ended up these boards were only used in the Attache computer - which was given the iCOM brand - not Altair. Since only one byte was altered (and simply forced to zero to suppress the banner), it’s possible this change was done to the ROM post production. Of course, this possibility depends on the type of ROM technology used.

Mike D