Also, as DD recording uses a higher recording strength than HD you can over set the magnetic state to a level where it is unchangeable, or unpredicatably effect adjacent magnetic grains, like pressing very hard with a pencil when writing. With an HD disk with 125000 magnetic grains along a track if you only do 62500 magnetic transitions you are depending on each magnetic tranisition exactly affecting exactly two magnetic grains. For example a 1.4 meg floppy disk can be formatted to hold 1.7 megs and 360k disk, when used in 1.2meg drive, can hold 830k. You can use it to format floppy disks to greater capacity than normal. Also, because they are smaller, the recording head has to use a lower recording strength as if the DD recording strength was used it would effect more than one magnetic grain at once. NFORMAT is a floppy disk formatter that lets you control many of the low level details of the formatting process and file system. To do that the magnetic grain sizes have to be smaller. Insert a blank floppy disk into the disk drive. In order to store 12500 HD data bytes on a track, you need 125000 magnetic bit domains on a track. matting prepares the disk no information can be written to its surface. Essentially, there are 62500 magnetic bit domains on a track. In order to store 6250 DD data bytes on a track the magnetic grains need to be a certain size. It allows you to use an internal 5.25-inch floppy disk drive to copy data from 5.25-inch disks in various formats over a USB cable to a modern PC. That's like saying if a screw that is supposed to have 30 threads per centimetre fails a quality test it is sold as a screw with 15 threads per centimetre. Option 1: Use the FC5025 USB Adapter and an Internal 5.25-Inch Floppy Drive A small company called Device Side Data manufactures an adapter called the FC5025. IIRC the only real difference between HD and DD is simply whether the disk passed the QA process.No, the disk is physically different. Tautology wrote:We used to do that all the time for unimportant disks (e.g. I think MartinBs explanation sounds better But. The head widths are defiantly different in the older and newer drives, however! And only accounts for a minor part of the issue. Now you go back to the 1mm wide track producing drive and try and read the 0.5mm track What you get is a wide head trying to read a 0.5mm track but actually reading the 1mm track, or what's left of it, as well! You start with a track, say a 1mm wide, and then you write over with a 0.5mm track. Now consider this: format a disc with a 40 track drive - then over write the files on a high density drive - now try to read that file on the 40 track drive. width of the head? And now consider a higher density drive - what would the head width be? If you take a 40 track drive and an 80 track drive - what is the size e.g. I've been reading the above thread with interest and have my own take on another possible problem - reading discs between PCs and Beebs - Could be wrong, however. MartinB wrote:I strongly suggest you pull up a sandbag and read this thread when you have half an hour to spare

Floppy disk formatting