<3.5" drives and (most) 5.25" drives use the same data rates. Now <admittedly most 3.5" drives are used at double density, but I really Wrong. The upper rate for 5.25 drive is 250kbit/S (DD) (1.2mb drives are special case). The lower limit for 5.25 drives is 125kbits/S (SD). the 8" are 250 (SD) and 500Kbits/S (dd). 3.5" drives accoring to the sony doc infront of me are 250kbits/S (DD) (720k) and 500kbit/S (1.44) (DD). The 1771 only does the 250kbits/S rate for 8" SD and the 5.25 floppy rate is 125kbits/S. I've tried the SD mode to 3.5" floppies and it's sorta useable but when you figure it out you don't get much for the effort and most of the 1771 based controllers do not deliver or check two sided signals. I have two and they don't! <can't see a good reason why you can't format a 3.5" disk single-density, <using the same data rate as for 5.25" single density disks, which the <1771 is quite capable of. It's half the pulse rate the drive read elctronics are designed to bandpass. <The actual pulse rate at the floppy drive interface is not very different <between single and double density operation. The single-density system <'wastes' half the pulses on clock pulses. Double density is NOT simply True but the peak shift is way different. To get something useful you need to run the 1771 as if it was 8", then use a format that put the right total number of bits on the media roughly 250kbytes a side. then you have an oddball format that noone wants to read (PCs will have fits without a tweeked controller) and will be questionable for the effort. Get a 1793 board and do it right and get some real storage for the effort. The CCS or Compupro boards (others too) are very nice and can be setup so the data rates are appropriate for 3.5" but using the 5.25 connector for the 34pin connector. Don't forget, the step rates for the 1771 class of controllers and drive were also slower than 3MS (more like 12-40ms) so if you going to fix that, the format and what else why not set up a real controller. Either that or learn to fix 8" drives and use them as media is still plentyful. After all I still keep an 8" SSSD format as that is the official CP/M standard. <doubling the read or write clock rate and leaving everything else unchanged Been there done that and have the NEC Tshirt for the 372 sd controller and the 765 all mode. Don't go there. I know the parts and the industry for the time frame very well and have plenty of examples and original docs here to refer too! this is one area where the archive is unusually deep. Allison