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Is it possible for a 400 to run a 16K OS ROM?


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I understand that the three OS chips on the 400 can only address 10K, but is there any reason why an Atari 400 could not run a 16K operating system? I'm thinking of tf_hh's "Atari 400 RAM-Card 48/52 KB & external OS-ROM". It has the option to run a 16K EPROM OS. Can this board run the 800XL's Omniview 80 16K OS since it based on the 400/800 OSB? If it does not mess with joyports 3 &4, could it work and if so, would it allow full access to 64K RAM?


The Omniview 80 OS is 16K

1) Based on the Atari 400/800 OSB OS ROM

2) Has the fast math floating point

3) Allows full access to 64K of RAM (Its a 64K OSB)

4) Has the ATR-8000 monitor built in

5) Has 80 column output



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My 400 has Supermon which occupies $C000-$CFFF so brings it up to 14K.


You can't override the IO area $D000-$D7FF which is 2K which is why the Self-Test Rom in the XL gets mapped to $5000 when switched in.

The logic and additional mod to do a 4K Rom addition at $C000 I think is fairly simple given that the 400/800 demux the address into 8K blocks to support the memory expansion architecture of the 800.

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