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

[Fred Cisin]

>From the FDC point of view, which doesn't have optical view of the drive 
and media, the 80 track DD 5.25" looks similar to a "720K 3.5" drive.
(80 tracks, 9 sectors per track, 300 RPM, 250K data transgfer rate)

On SOME PCs, setting the CMOS floppy setting to "720K" may take care of 
it.


On Tue, 22 Feb 2022, js--- via cctalk wrote:

>
> On 2/22/2022 6:42 PM, Warner Losh wrote:
>> 
>> On Tue, Feb 22, 2022 at 4:36 PM js--- via cctalk <cctalk at classiccmp.org 
>> <mailto:cctalk at classiccmp.org>> wrote:
>> 
>>
>>     Rod,
>>
>>        Not sure an RX33 (if 1.2MB
>>     equivalent) would write working RX50
>>     800k (double density) disks.  Very
>>     different drives.
>> 
>> 
>> The RX-33 is the same sort of drive that you had in your PC if you wrote
>> RX-50s with your PC. Back in the day, lots of people used RX50.SYS to
>> have it setup the transfer rates, RPM and sectors per track parameters
>> so that you could read/write them on a PC running DOS. The parameters
>> are basically the same ones you need to write the 360k DOS floppies, only
>> with twice the number of tracks and 10 sectors per track instead of 9 (this 
>> is
>> done by making the track gaps smaller and eeking an extra sector out of the
>> deal, but using at the same data rates).
>
> Thanks for reminding me, Warner.  To recap:
>
> The format used on a RX50 disk is:
> Single Sided, 80 tracks, 10 sectors per track
> 96 TPI, 300 RPM, 250 KHz data rate
> ... which translates to 400K SSQD.
>
> The format of a high density 5.25" PC disk is:
> Double Sided, 80 tracks, 15 sectors per track
> 96 TPI, 360 RPM, 500 KHz data rate
> ... which translates to 1.2MB DSHD.
>
> So to use an actual RX-50 on my PC, I just had to use an FDC capable of 
> slowing down the data rate, and make a floppy cable to route the signals 
> properly (minor changes from a PC floppy cable).
>
> What Rod *might be* running up against with using PUTR and his RX-33, is that 
> his RX-33 RPM and data rate might not be slowing down to equal that of the 
> RX-50... which could be an FDC problem.    Does the RX-33 automatically slow 
> the RPM if the data rate drops to 250khz?
>
> - John Singleton
>
>
>
>>        I've successfully put an actual
>>     RX-50
>>     drive on my PC, and written RX-50
>>     images
>>     using PUTR.  You might try that route.
>> 
>> 
>> Did you have difficulties with Pin34 not being the change disk pin? That's 
>> what
>> I ran into when I tried this many many years ago...
>> 
>> Warner