Current source for RX50 media?

Warner Losh imp at
Sat Jun 25 01:15:58 CDT 2016

On Fri, Jun 24, 2016 at 11:54 PM, Warner Losh <imp at> wrote:
> On Fri, Jun 24, 2016 at 10:20 PM, Ethan Dicks <ethan.dicks at> wrote:
>> My usual 5.25" drive (I have several) is the Teac FD55GFR - strapped
>> for RX33 use with DEC controllers or strapped slightly differently for
>> PC use (I know the directions are floating around)
> The RX-50 is a 80-track version of the 360k IBM-PC 40 track floppies.
> It was formatted at 10 sectors per track with smaller inter-sector padding
> bytes than normal. It uses the same rotation rate and data transfer rate
> as the older drive, which is different than the AT formatted floppies
> use.
> So RX-50's use 250k transfer rate, 80 tracks, usually 1 side (though
> the controller supports 2 sides, the physical RX-50's don't). 512 byte
> sectors. 16 bytes between sectors (as opposed to either 35 or 42
> for IBM-PC floppies) with 46 bytes format gap (as opposed to 80
> for IBM-PC floppies). This is how you got 400k out of a single sided
> 80 tracked disk. IIRC, the rotation rate is 300 for RX-50 and old
> IBM-PC vs 350 for the IBM-AT drive. All these niggling differences
> cause problems...

I was looking at the wrong row in my tables. The RX-50 uses the
300K transfer rate, while the 1.2MB IBM-AT floppy uses 500k. The
rotation rate is different, but I'm having trouble locating that. Sorry
for the possibly bad info. I added support for RX-50 to the FreeBSD
driver (preliminary, mostly works for reading, writing has issues and
formatting doesn't work) several years ago, so I needed to know...


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