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PC JR SW compatibility w/ IBM PC, XT, AT

Shadow Lord

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Hello all,

I found this excellent page by none other then our own mbbrutman discussing the problems of running PC SW on a PC Jr. However, what about the other way around? Could PC Jr. SW run on a PC? Or did the "better" sound and video support prevent that from happening? If so, anyone know of a PC Jr emulator that will run on a DOS machine (either AT or a 486)? Thanks!
 

krebizfan

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Shadow Lord

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Thanks for the info. So if I am only interested in a PC Jr game then I should be able to run it (minus fancy colors, sound) on a regular IBM AT? I will have to try TandEm just to see how good/bad the PC Jr graphic sound was.

Edit: Checking the TandEm doc it does not emulate the PC Jr at all. It was meant to but it seems as if they never put in the support for the ROM. I'll have to see if MESS has an archive.
 

mbbrutman

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The PCjr video modes and the PCjr sound chip did not get picked up by any other machine or card except for the Tandy series, which was designed to be compatible with the PCjr on those two features. So while an EGA or VGA card is certainly capable of doing a similar screen mode, the actual mode number is not available.

PCjrs also have a trick where you can address the first 16KB of the video buffer using the addresses at B800:0000 (CGA) even though the memory is in the first 128K on the machine. This is great for CGA compatibility, but when you use the higher screen modes that require more than 16KB you have to do the addressing to touch the bits yourself. No later (or sane) video hardware is going to be able to emulate that behavior. (I'm not sure how Tandy games do this; they should have the same problem. Which is why the software probably asks if you are on a Tandy or PCjr explicitly, or tries to detect it.)

The best solution is to own a PCjr, or to find a decent emulator. Tand-em never worked for me. The MESS emulator has some PCjr features, but it's not perfect yet. (Working with them is on my todo list after the next FreeDOS release gets out.)


Mike
 

Shadow Lord

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The best solution is to own a PCjr, or to find a decent emulator. Tand-em never worked for me. The MESS emulator has some PCjr features, but it's not perfect yet. (Working with them is on my todo list after the next FreeDOS release gets out.)

Mike

Mike,

Thanks for the info. I am only interested in running one game so a PCJr would be over kill. I looked at MESS and the last version that ran on DOS was from a few years back. When/if you do your updates will there be a MESS DOS version with these updates or will we be limited to a windows version only?

EDIT: Mike, as an aside any ideas when FreeDOS 1.2 will be out? I know 1.1 is in testing now but 1.2 seems to be the version w/ the feature set to be run on a modern computer (USB support, built in networking). Also will there be proper LFN support? I know LFN is currently provided through a TSR but can it be baked into the kernel, be more stable and work across a wider array of programs (as i recall that TSR was very flaky and was never really developed to far). Thanks.
 
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