My guess is that your primary controller isn't releasing the IRQ and DMA lines when bit 2 in port 3f2 is cleared. Not all controllers do. If this happened to our customers, we usually told them to use a different DMA and IRQ for the second card and adjust their DISKETTE.CFG file accordingly. We used to offer a diskette copyring program (SyDupe) that could use up to three controllers all on different IRQ and DMA to achieve three completely overlapped data transfer paths (i.e. we'd write three diskettes at the same time). This worked for 720K, but 1.44MB put too much of a strain on most ISA bus implementations to be a reliable product. Still, it was kind of neat to see the product working with a loaded (12 floppy drive) system. Cheers, Chuck