Compatibility

The Advance 86 wasn't totally IBM compatible. Because it used an 8086, with a 16 bit data path, extra logic was needed to make the 8259 interrupt controller respond on the correct ports. They didn't do this, so where a real IBM compatible would use ports 20 and 21, the Advance only used even numbered ports$ in this case, 20 and 22. Any software that programmed the interrupt controller would not work correctly. Advance provided a conversion program that (mostly blindly) changed 21 to 22 in executable files. Not a success. I did it by code inspection with DEBUG, and was usually successful.

Compatibility