Current source for RX50 media?

Warner Losh imp at
Sat Jun 25 00:15:42 CDT 2016

On Fri, Jun 24, 2016 at 10:13 PM, Fred Cisin <cisin at> wrote:
>>> 2) It's been too long so I don't remember, but don't you use normal pc
>>> floppies (5.25) and PUTR can format them?
> On Fri, 24 Jun 2016, Ethan Dicks wrote:
>> Yes, but you need the right type of PC floppy because RX50 are
>> single-sided and 80 tpi and 10 sectors-per-track (400K on one side).
>> I'm sure there are FAQs and instructions all over about the process...
>> I just don't recall off the top of my head which keywords to shop for
>> that are merely good enough for TRS-80s and C-64s and which will do
>> for RX50s.  Single Sided Single Density will not cut it, not that uber
>> cheap floppies abound these days (Elephant?  BASF?  Only if you like
>> cleaning your heads between each diskette).
> That would be 80 TRACKS at 96 tracks per inch.
> Those would be the 300 Oersted disks, same diskettes as "360K".
> Do NOT use the 600 Oersted "1.2M"/"HD" disks.
> Being Single Sided, it really won't hurt to use just the first side of a
> Double Sided disk.

Single vs double sided doesn't matter.

> 80 track V 40 track both call for the same chemistry of the coating, but you
> should probably bulk erase whatever you get.

40 track raw media sucks in an RX-50 drive.

> If you use a PC to format them, the requirements are essentially the same as
> for a "720K" 5.25".  Formatting can not be done with a "360K" (40 track)
> drive, but can be done with a 1.2M drive, or with a 720K 5.25" (which aren't
> common in the PC world).
> There are a couple of potential complications to using a 1.2M drive, that
> can be gotten around in software.
> (96tpi track spacing,
> same write current, rotational speed and data transfer rate as for 360K)

The controller for the PDP-11 can't format them. The Rainbow can format
them w/o problems. You won't be able to use PC formatted 5.25" drives.
The IBM AT 1.2MB floppies can be reformatted and perform adequately,
but it's much better to use the proper quad density disks. By "adequately"
I mean "in a pinch until you can get something better because the data
is at risk" Some of the disks I used back in the day worked OK, while
others didn't work so well.

> We all have our favorite and hated brands.
> Ones you buy now, would likely be used or New stale stock, but that probably
> won't be a problem if they were stored well.

Yea, I haven't bought new media in 15 years. My old stuff still works
well enough...


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