RT-11 was officially supported on the PRO series.  The PI(X).SYS handler was the interface to the PRO specific hardware. 

-Steve

SF:IP2

> On Oct 23, 2022, at 10:56, Paul Koning <paulkoning@comcast.net> wrote:
>
> 
>
>> On Oct 22, 2022, at 5:54 AM, Johnny Billquist <bqt@softjar.se> wrote:
>>
>> Well, obviously COPOS/11 isn't P/OS, as you later noted. :-)
>>
>> P/OS was the OS for the DEC Professions. Came in three models. 325, 350 and 380.
>>
>> The 325 and 350 were F-11 based. 325 only had RX50 floppies, while the 350 had a harddisk.
>> The 380 used the J11 CPU, but sadly at a low speed and without cache. And all software had to work with the F11 as well, so none of the J11 improvements were used.
>>
>> Basically, the Professional was a good idea implemented rather badly.
>
> Its main problem was that it had a completely different I/O bus and I/O architecture.  And a lot of that went poorly because Intel chips were used for it, and Intel rarely if ever has good design for anything.  The interrupt controllers, for example, are a mess.  Fortunately, most of its misfeatures are not used on the Pro (like edge-triggered interrupts).
>
> The biggest blunder was a set of storage controllers without DMA, even though the bus actually supports DMA according to the documentation.  So the hard drives -- not very fast to begin with -- have to be 4:1 interleaved to avoid missing the next sector after an I/O is done.  That's true on both F-11 and J-11 based machines, so clearly the CPU speed is not at fault.
>
> On the Pro 380, a pile of discrete chips were replaced by one or two gate arrays (so many of those Intel chips disappeared, but not their ugly APIs).  Apparently, the designers made the I/O gate array at 10 MHz, and made it synchronous with the CPU clock on the assumption that Harris would deliver its promised 20 MHz J-11.  When they did not (18 MHz was the best they could do), the Pro 380 was forced to run the CPU at 10 MHz instead.
>
>> And P/OS was a very bastardized version of RSX-11M-PLUS. Again, a good idea done badly. Menu driven, and weird. And not entirely compatible with the rest of the RSX family.
>
> There was also a Pro RT-11, I don't remember if that was an official product or a midnight project.  The RSTS port was definitely a midnight project.
>
> And there were two Unix projects.  I never remember which is which.  One made it to field test -- I had that on my home machine -- but it was canceled before the actual release,  Then a different PDP-11 Unix was shipped instead.
>
> The field test one had some really weird hacks: I remember a "vi" that didn't update the screen while you were typing, instead you had to hit some special key to force the refresh to happen.  My guess is that it was a performance issue, but that seems strange because other software had no trouble doing that sort of thing.
>
>    paul
>
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