On 9/3/2012 8:15 PM, David Empson wrote:
Charlie<charlieDOTd@verEYEzon.net> wrote:On 9/3/2012 3:53 PM, D Finnigan wrote:J. Vernet wrote:As I remember, it's not a drive harware issue but a controler hardware issue... In an USB external floppy, there is an USB controler that do not let the drive being used in 800k (variable rotation speed).It's very likely that the drive can't spin at more than one speed, that the motor is fixed. As far as I know, only Apple computers had variable-speed 3.5" floppy drives. These were manufactured by Sony. The Apple drives used GCR at their lowest level, whereas the IBM drives used MFM.I believe the 3.5" Apple drive can read/write either GCR or MFM if the controller is designed for both. Consider that a normal 3.5" Apple drive when connected to a PC Transformer can read/write 800K ProDOS disks and 720K MSDOS disks that are compatible with IBM clones. Note also that with the 720K disks the floppy drive speed doesn't vary.The Apple 3.5 Drive (800K model) has the variable drive rotation speed as a built-in feature,
I agree, but apparently it can be disabled by the controller since the PC Transporter manages to do it for the 720K MFM disks.
unlike earlier Macintosh 400K/800K drives, where the rotation speed was controlled by a timing signal from the Mac. If the Apple 3.5 Drive is used with a PC Transporter to access 720K disks, the disk controller on the PC Transporter has to cope with variable bit cell timing depending on which range of tracks are passing under the head. I don't recall whether I used that capability much, but I expect it would be somewhat unreliable for writing, and not too bad for reading.
Mine works flawlessly for reading and writing *if* the disks are formatted on a PC or pre-formatted. If they are formatted on the PC Transporter they still work flawlessly if they are used only with the PC Transporter card. The only problem I've found is when a disk is formatted on the PC Transporter some PCs (less than half of those I've tried) have problems with those disks.
Charlie