Least PC-Compatible MS-DOS machines?

On Fri, Jun 6, 2014 at 8:44 PM, Chuck Guzis <cclist at sydex.com> wrote: I agree; that is amazingly strange. I used three different brands of 8-inch floppy controllers for the Apple back in the day, from Sorrento Valley Associates (SVA), Vista, and one other that I don't recall. All of them used standard IBM 3740 FM and the two that did double-density used IBM System/34 MFM formats, with no Apple influence. The ROMs on those controller were capable of patching Apple DOS RWTS to support the 8-inch drives, but in doing so they bypassed all of the normal RWTS code. They would jump back into RWTS if the slot number didn't match that of the 8-inch controller, so that the 5.25-inch drives behaved normally. The big problem was making an 8-inch floppy controller coexist with any hard disk controller, which also wanted to patch RWTS; I had to hack that up myself for my system. Presumably if one had floppy and hard drive controllers from the same vendor they would have dealt more gracefully with such a configuration. Apple solved this (for the most part) with ProDOS by standardizing a per-slot disk driver vector table in the system page, and in their spec for disk controller ROM entry points.