Cromemco 4FDC, How do you format a disk?

<> work. The 5.25" floppy single density rate of 125kBITS/sec clearly would <> fall below the spec. There are limits to the write pulse width as well < <You are still missing the point, totally... < <125kbps FM is _NOT_ 125kpulses/sec at the disk interface, as you seem to <be implying. I'm not missing anything. For FM that means the two frequencies are 125/250KHz. For MFM that is very not true. Different bandwidth, but still not in the range of the accepted 250kbits/sec of the sony. <Double Density, MFM, 250kbps. <----------------------------- <A bit cell is 4us long, so 250000 of them per second. There is a (data) <pulse in the middle of a bit cell written as a '1', no (data) pulse in <the middle of a '0'. There is a (clock) pulse written at the start of a <bit cell if there is no (data) pulse in both this bit cell and the <preceeding one. Your missing bis/time vs frequency domains/bandwith. <For MFM you need to be able to record/reproduce pulses with separations <of 4us, 6us, 8us. true and for the data I gave the 125kbits/sec rate is too low. As it's minima was 250kbits/s is twice that! Part of the recording scheme is that there are rules for continous strings of 1s and 0s, they arent permitted to exist for clocking and bandwidth reasons. <Oh, absolutely. But the FM at half the data rate meets that spec. It has <to. I am not suggesting you could feed 300 baud data into a disk drive <and expect it to work - it almost certainly won't. FM at half the data rate is the 8" SD rate of 250kbits/sec... not 125k! The 125kbits/sec is the 5.25" floppy single denity rate. The problem is that the 2f domain is in the right range but the base rate is clearly not. It's an off by 1/2 problem. The 3.5" drive was designed to reproduce pulses that fall in the 250khz (minima) to 1.0mhz rate(maxima) so theres the bell curve that your skirting using the 5.25" single density data rate. The 8" rate 250kbits/S lands right in the range but rotation time being different you need a different sectoring arrangement. Allison