Simulated disk drive for RT-11?

Allison ajp166 at
Fri Jun 3 14:43:30 CDT 2005

>Subject: Re: Simulated disk drive for RT-11?
>   From: Ethan Dicks <ethan.dicks at>
>   Date: Fri, 03 Jun 2005 12:39:28 -0500
>     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at>
>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.

RSP and MRSP are stock firmware.  But as you said it's poorly 
documented even in the EK-OTU58-TM-002 tech manual I have.

>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

At 256k per drive it's essentally an RX01 only slower.  For RT11
thats a usable configuration.  

One trick to speed things up is if the CPU has enough ram (256k is 
enough and 1mb really works) is to run the RT11 VM: driver that's
the virtual disk driver (ramdisk).  Load it with a copy of 
everything then boot it then the tape/tu58 becomes seconday 
storage and you have more space.  Makes using a TU58 much 
friendlier.  The boot time for that is rather long.

>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.

There is a PC/DOS version that emulates a TU58 using the PC as a 
disk rather than tape.  I think Bob at sparetime gizmos has the code
but I could be wrong.  


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