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Does the Sun-4c PROM 2.X *really* have a 1.X compatibility mode?

AstridRedfern

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Oct 19, 2022
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This post follows on from discussion in https://forum.vcfed.org/index.php?t...-gx-hardware-e-g-sparcstations.1240578/page-2 - in which @tokenalt mentioned that they couldn't run SunOS 4.1 or earlier on their 4C because it had PROM 2.X.

One of the places I went to in search of a PROM 1.X file was forums DOT sgi DOT sh. And a user (the owner and main admin, I think!) of those forums posted this quote from Discord chat:

actually, you don't strictly need a version 1 .X OBP to run SunOS 4.0. There is some documented OBP magic you can use to enable 1.X compatibility on a 2.X OBP version. It is pretty much just an environment variable (that I currently forgot...).

(I don't know what OBP stands for. Maybe "onboard PROM".)

Does anyone know anything about this magic, this environment variable, and how to enable 1X compatibility mode? And are there any limitations to its compatibility? (that you know of.)

Thanks to anyone who can help,

Astrid.
 
@Al Kossow Thanks for that.

Thanks also for uploading your copies of Aviator 1.2 and the trial version of 1.5.1 back in 2019 - hope you saw the 1.5.1 footage and it brought back some memories!
 
Try typing old-mode at the "ok" prompt.
You would probably have a good chance of this working on sun4c or older sun4m (Sparc 10 or maybe older Sparc 20). I'd be surprised if it worked on a Sparc 5 or Sparc 4.
 
old-mode is present on my ss10 and ss20 but it's just a forth script to make the interface appear like sunmon, it's not an actual compatibility mode. In other words it's for human convenience not software compatibility. Maybe on a sun4c machine old-mode is a real compatibility mode but I don't have the hardware to test.
 
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