Loading BIOS from dos debug - possible ?

This will not really work. Even if a real mode booted DOS had the requirements to execute the BIOS and if you would know the entry point of the BIOS, your problem is still that the BIOS expects to be located at F000:0000 in memory and therefore contains many hardcoded references to the F000:xxxx memory region. However, this memory address space is used already by your old BIOS and the F000:xxxx memory cannot be written. Even if it could be written, you would still run into trouble, since the hardcoded memory references in your new BIOS wouldn't match the ones in your old BIOS. Even if they would match, your would be executing parts of your old BIOS, which would be a bad idea for testing.

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You might cosider getting a "Gigabyte" motherboard the next time. They have a Dual-BIOS feature which means you have two BIOSes and you can select from which BIOS to boot. I even "modded" my BIOS in the knowledge that I could restore the old BIOS in case my code wouldn't run. But it worked fine.