24 Oct
2022
24 Oct
'22
2:03 a.m.
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(a)comcast.net> wrote:
On Oct 22, 2022, at 5:54 AM, Johnny Billquist
<bqt(a)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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