On 07/17/2018 04:11 PM, Eric Smith via cctalk wrote:
When 3.5-inch floppy drives and hard drives were introduced, most used the
same 34-pin interfaces as their 5.25-inch counterparts.
On Tue, 17 Jul 2018, Chuck Guzis via cctalk wrote:
Can't say much about 3.5" hard drives (the only really early ones I've
seen are standard ST505-type 2-cable interface).
I interpreted Eric's comment as meaning that the 3.5" hard drives used
same interface as the 5.25. inch hard drives (34 pin and 20 pin), and the
3.5" floppy would be same as 5.25" floppy 34 pin.
But initially, the 3.5' floppies used a 26-pin interface (13 signal lines):
http://bitsavers.informatik.uni-stuttgart.de/pdf/sony/floppy/Sony_Micro_Floppy_Disk_Drive_Model_0A-D30V_OEM_Manual_Mar82.pdf
And of course, the drives spun at 600 RPM, which was really nice if you
were used to 8" or 5.25" drives. The Drivetek 5.25" high-capacity
drives would also spin at 600 RPM when a conventional floppy was
used--again, a nice feature.
Could the Gotek firmware, and some drivers on PC's with "HD" or "ED"
controllers, be kludged together to get faster data transfers?
ALthough the early 3.5" were 600 RPM and 26 pin, they soon changed over to
34 pin. (some MS-DOS 2.11 laptops) I'm assuming to make them a drop-in
replacement for 5.25".
But, yes, when first introduced, they were not yet 34 pin.
And, of course there were a few 5.25" drives that were not the standard 34
pin interface, such as Apple. (SA390 (SA400 without the "logic" board"))
My first "1.2M" 5.25" drive (Mitsubishi EARLY 4854?) had a 50 pin
connector! That made me think that they were targetting 8" replacement,
rather than 5.25" storage increase.
Unsubstantiated story from a Microsoft person was that during the initial
stages of AT-BIOS and DOS 3.00 programming, they thought that there was an
8" machine coming.
3" and 3.25" were also almost completely compatible with the "standard" 34
pin interface. Although I remember one drive that had 5V and 12V swapped
in its 4 pin power connector! And my 8" drives did not standardize power
connector and requirements.
