Erno.Palonheimo@Hut.FI wrote:
> do disks other than those of RD5x series work on a RQDX3?

Only if they're completely equivalent to an RD5x drive, which for the
most part means only the same OEM drive, sometimes with a special jumper.

The Maxtor XT2190 works fine as an RD54.

> And, what is the actual disk interface?

AFAIK there's no official name for the interface, but it's widely known
as "ST-506" (the model of the first Shugart Technologies drive that used
the interface) or "MFM" (the channel code used, which isn't really a proper
way of identifying the interface, as MFM recording was also used with many
other interfaces).

> I have quite some old ESDI disks which vary in size from 300
> megabytes to one gigabyte.

Not gonna work on an RQDX[123], unfortunately.  There were third-party
ESDI controllers.

> And, what can you
> actually mount on the slot that's sideways on the BA123 chassis? Will a
> TK50 work if mounted sideways? How about an RD54?

The Maxtor 2190 is rated for operation in either a horizontal or vertical
orientation, as is the case with most "ST-506" drives.  Note that this does
*NOT* mean that it can be used in any arbitrary orientation (e.g., 15
degrees from horizontal), as that puts different dynamic loading on the
bearings and will cause it to wear out faster.

Personally, I've only used the vertical slot in the BA23 for floppy drives.