Simulated disk drive for RT-11?

Ethan Dicks ethan.dicks at
Fri Jun 3 12:39:28 CDT 2005

On 6/3/05, David Betz <dbetz at> wrote:
> Does the TU-58 use a standard RS-232 serial interface?

Yes.  The TU58 drive is strappable, but 38Kbps is a standard speed.

> Is the protocol defined somewhere?

Yes... I know it's written up in several DEC manuals, some of which
are probably on bitsavers.  The basic protocol is called "Radial
Serial Protocol" (RSP), but, I think, for newer implementations, like
in the firmware of a VAX-11/750, there are some variations that, while
documented, aren't as easy to find as the base documentation.

It's ordinary to hook a real TU58 on a port of a DLJ11J... one can
even use a straight-through 10-pin Berg cable - it's the same pinout
(one of DEC's standards).  It's also possible to emulate a TU58 on a
modern PC, or to hook up a real TU58 to a modern machine to read

I don't have my tools with me, but googling for TU58 and emulator will
probably cough up something interesting.

Media size is a bit of a problem - a real TU58 is kinda small, even
compared to an 8" floppy.  Speed isn't great - at least an emulated
drive doesn't have seek delays, but transfer speed becomes the

OTOH, there are drivers for RT-11, and it _is_ a simple device to
emulate.  If only it were a few megs in size, it would be adequate for
quite a few applications.

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