Hi Guys, I've found about 6-7 systems around here that work fine with ImageDisk and single-density. I've also tested all of my systems using Chucks handly little TESTSD utility ** and I get an exact match - the systems that work with IMD and single-density are reported OK by TESTSD and those that don't work with IMD and single-density are reported as "failed" by TESTED. ** for those who are unfamilier with it, TESTSD formats the top 5 tracks of drive A as single-density and verifies that it can read/write it. You can easily make up a floppy that you can boot and use to test for single-density (thanks Chuck). I also have corresponded with quite a number of people who have gotten IMD and single-density to work on other systems, so I know that it is basically functioning correctly. I've been corresponding with a chap who has been trying to get IMD to work at single-density without success. I gave him the TESTSD utility to check out his systems, and also mentioned that I have heard "good things" about Adaptec controllers. This is his response: ----------------------------------------------------------------------------------------------- I tried two adaptec controllers I had here. The first - an Adaptec 1542CF wasn't reported as compatible by the TESTSD program, and doesn't work. The second, a simpler Adaptec 1522A is reported as compatible, but doesn't write the Osborne SD 5.25" format using IMD. Interestingly however it will write it using Teledisk. It also will read correctly with Teledisk, but not with IMD. Strange stuff! It uses a DP8473AV as the floppy drive controller IC. For completeness I'm using DOS7.1, and a Celeron 300A system and a Qume 5.25" 360Kb floppy. ----------------------------------------------------------------------------------------------- (Osborne SD disks read/write OK for me in all of my IMD systems) So it would appear that I am still missing something. Perhaps it is something specific to the DP8473AV FDC, or some other PC hardware specific setting that "happens" to be set correctly by BIOS in most cases. IMD configures the FDC as per the original NEC 765 databook. It also sets the drive motor and select signals at port 3F2/372, the AT data rate at 3F7/377 as well as the DMA controller/setup... Anyone have any idea what I have missed? My main references have been the NEC databook, and the Phoenix BIOS technical reference manual ... Regards, Dave -- dave06a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.parse.com/~ddunfield/museum/index.html