Floppy disks again

Hi Bill, First off, 3:30 in the morning is too early to be reading mail. Go to bed :) Most of my knowledge is from hard disks, but should apply OK. Basically, magnetic media is a tradeoff between coercivity (how easy it is to flip the bits) and write current (how hard you have to try and flip the bits). A material with high coercivity resists being re-magnetized in a different direction. The more write current you push through the head increases the electro-magnets power, but also increases its SIZE. More write current means you are writing bigger transistions. Remember, you can't read a 'north' as a one, you can only detect when the 'north' changes to a 'south' (a transistion). Ok, so 48 TPI media has low coercivity, so a 96TPI head with higher write current will cause the adjacent tracks to erase because of the magnet fringes from the head. These magnetic fringes aren't strong enough to effect 96TPI media because it has a higher coercivity. Finally, the head controls the size of the track. The width of the magnetic poles sets the width of the track written, plus a little fringing to provide track erasing to clean the previously written data in case of track misalignment. The bit density is controlled by how fast the head is moving w/respect to the media, and how fast you can toggle the write current. Think of it this way: if you have a stencil .1x.1 and can fill it in in either red or blue. put the stencil down and fill it in red. now move the stencil 1/3000 inch. put the stencil down and fill it in blue. repeat a LOT. Now you have 10 TPI at 3000 bits/inch. Make sense? I will look for a picture from a class I took many years ago and put it somewhere. I think I still have a geocities webpage :) clint On Tue, 12 Oct 1999, Bill Yakowenko wrote: