24 Oct
2022
24 Oct
'22
3:36 a.m.
On 2022-10-23 16:56, Paul Koning wrote:
True. But even the fact that they decided to make it incompatible with
all previous PDP-11s were a bad decision. No matter what chips they used.
It was also a bit of a midnight thing, but less midnight than RSTS/E.
RT-11 did actually ship with the required files to run on the PRO for a
number of versions, but it was removed in the last releases, if I
remember right. However, if you had an older kit, you could just take
those bits (I think mainly drivers) and use them with the latest version
of RT-11 and all worked fine.
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.
That they don't use DMA is a mystery to me. Maybe some problems with it?
I don't know of a single option that uses DMA. Anyway, I believe an F-11
and a J-11 running at 10 MHz will pretty much perform rather similar. So
the 4:1 interleaving, which obviously have to do with CPU speed, is
another sign of the problems with the system.
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.
As far as I heard/know, the gate array was limited to 10 MHz. Wouldn't
have mattered how much faster the J11 could run. In the PRO-380, it
would never be run at more than 10 MHz.
And I think it sounds weird if the fact that the J11 only reached 18 MHz
would be a reason to limit the PRO to 10 MHz. Why not run at 18, or 15,
or whatever? The gate array needs to run at the same speed as the CPU,
so it couldn't be scaled or anything either.
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.
VENIX was the commercially available Unix.
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.
So many strange things around the Pro. Good idea; bad implementation.
A desktop PDP-11 with graphics... I would have liked that. The Pro - not
so much.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt(a)softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol