VAX Q-bus identical to PDP-11 Q-bus?

Paul Koning paulkoning at
Thu Dec 7 11:44:05 CST 2017

> On Dec 7, 2017, at 11:50 AM, Jon Elson via cctalk <cctalk at> wrote:
> ...
> MSCP is a software protocol.  Any device that has a driver available for the PDP-11 operating system you want to use can use that device.  

True with small variations.  A sufficiently large disk might not be supported on some OS because the on-disk structure is limited in what device size it can handle.  (This applies to RSTS for example.)  Some devices use obscure MSCP mechanisms that might not be in all drivers -- for example, the RA80 uses host-based bad block replacement, which is quite a complicated process; I know RSTS supports that but it might be omitted in some other operating systems.

Also, in DEC terminology, "supported" doesn't mean "it works in the software" but rather "we stand behind it".  That means tested, sold, handled by product support and field service, etc.  For example, the RP07 works in RSTS on an 11/70, but it is not "supported".  I'd expect the same is true for any number of MSCP or TMSCP devices that were intended to be sold only on VAXen -- they may very well work, but if you had plugged one in on a machine where they aren't supported, DEC would give you no help with any problems.


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