Installing an operating system on the 11/83 - update.

[Fred Cisin]

DD 5.25" disks are about 300 Oersted.
HD 5.25" disks are about 600 Oersted.

If you use HD disks to write DD content, the data fades away real fast.

However, on 3.5" disks, the difference is more like 600 Oersted VS 750 
Oersted, and you may get away with using the wrong disk.

360K disks are tested/certified for 40 track (48tpi) double density. 
Although not tested/certified for 80 track 96tpi, the cookie is the same, 
and they generally can handle 80 track (96tp) double density just fine. 
Disks of extremely marginal quality (such as Wabash, or pre-Datalife 
Verbatem) can still give you troubles.


In general, commercial 1.2M drives are also intended to be able to 
read/write(with track width problems!) 360K disks.  So, if the write 
current is at the "360K" level, and you get the data transfer rate correct 
(250K at 300RPM or 300K at 360RPM), and you get the drive to NOT "double 
step", then you can, indeed, read/write 80 track DD disks using a 1.2M 
drive.

Using a double density 80 track drive, such as the the Tandon TM100-4, 
Shugart/Panasonic/Matsushita 465, or the Teac 55F makes it a little 
simpler/easier, since those drives don't HAVE multiple write currents, nor 
360RPM, so just let the PC FDC think that it is a 360K drive (other than 
being 96tpi with 80 tracks), and the other issues aren't there.

10 512 byte sectors per track is similar to the 8 or 9 sector per track PC 
track format, other than squeezing an extra sector onto each track, by 
redducing the sector gaps.  Readily doable with INT13h (plus INT 1Eh), and 
not even having to talk directly to the FDC.

--
Grumpy Ol' Fred     		cisin at xenosoft.com

On Wed, 23 Feb 2022, Ray Jewhurst via cctalk wrote:

> I read that you can indeed use a standard 1.2 Meg drive and that you can also use DSHD 5.25 disks in place of RX50s. Is there any truth in this? If there is it will be much easier and cheaper to make disks for my Rainbow.
>
> Sent from my Verizon, Samsung Galaxy smartphone
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