On Mon, 3 Sep 2012, J. Vernet wrote:
The original Apple II drives were stripped down versions of a "regular drive", so it could be controlled by the Apple II and the data fed more directly to the head.Le 03/09/2012 17:38, Michael Black a écrit :On Mon, 3 Sep 2012, J. Vernet wrote:No USB Floppy drive will read 800k floppy.I thought that was the primary issue, hardware. INitially the Mac drives were single-sided, 400K. Then double-sided, 800K. Then a period where they could deal with 800K disks, and 1.44K disks, ie "IBM compatible". Then a period where the drives had the hardare for the 800K disks, but apparently failed at the task (though perhaps that was sofware issue? I don't know.) And then no more ability to read 800K.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). I do not know if the last G3 "beige" can read 800k drive. I have one wich do not even read 720k DOS floppy... All Powerbook 1X0 wan read 800k Prodos, but my Wallstreet can't.
The early Macs used the same sort of thing, but then when the "superdrives" came along, they had to be special drives to be compatible with both, you couldn't take an "IBM compatible" 1.44K drive and plug it into a Mac.
And people have said there was a later period when the drives were supposed to be able to deal with 800K floppies, but didn't, I read that to mean the circuitry was there but some bug, but it didn't matter since by then few needed to deal with 800K drives.
Then the next batch of Macintosh drives dealt only with 1.44K floppies, no access to 800K. They still weren't "standard 3.5inch" drives since the interface was different, but they no longer had the circuitry to deal with the older floppy format.
So by the time the USB drives came along, the ability to read old floppies had already been eliminated, so why bother with the cost?
You're right, the USB floppy drives would have to have some level of controller inside the drive to go from USB to whatever the drive is doing, but I can't see the actual floppy drive being a dual type at that point.
A different way of looking at it is that you can't read Apple II disks on "IBM compatible" drives, at least not without a lot of software processing if then. That's because the drives don't access the floppy at the same low level that the Apple II drives did. After a while, the Macintosh drives became like those.
Michael >
I'm using an SE/30 for writing PRODOS 3.5 floppy, with an external 800k drive (more accurate 800k write).J. VERNET