Pierre, maybe someone else will provide practical experience with the combination QD32 & 11/23, but my first guess would be that bandwidth is not a problem: as long as all devices on the bus obey all the bus specifications, they should be compatible. Was your friend possibly talking about address width (in other words, the number of address lines on the bus)? - There are three variants, with 16, 18, or 22 address lines. Incompatibilities can arise if a *DMA controller* drives *less* address bits than the system actually uses. Non-DMA controllers have no problem because they never address memory themselves. A typical problem of this type is the RXV211 (RX02 floppy disk controller: DMA, 18 address bits) used in a 22 bit system. The problem can be circumvented in driver software by reserving a buffer area in the lower 256kB of main memory. IIRC, older versions of the 11/23 drive 18 address lines, making them capable of using up to 256kB (or 128kW) of memory. Later models (in particular, the 11/23-PLUS) supply all 22 possible address lines, allowing for up to 4MB (2MW) of RAM. I was told several years ago that some /23s can be upgraded by adding a couple of wires (and maybe a handful of bus drivers). The QD32 is no doubt a DMA controller, but I think I know it is 22 bit. Hence, it should be possible to use this controller in any Qbus system. Also IIRC, the QD32 uses MSCP to communicate with its driver software, so it should not even require any special software: a vanilla DU driver would be OK for RT-11 or RSX-11, for example. Anyone have better information to correct me? Regards, Andreas P.Gebhardt(a)gmx.de wrote: -- Andreas Freiherr Vishay Semiconductor GmbH, Heilbronn, Germany http://www.vishay.com _______________________________________________ cctech mailing list cctech(a)classiccmp.org http://www.classiccmp.org/mailman/listinfo/cctech