VAXen and minimal memory (was Re: The PDP11/04 has landed..)
Jerome H. Fine
jhfinedp3k at compsys.to
Thu Feb 11 19:39:32 CST 2016
>Rich Alderson wrote:
>From: Jerome H. Fine
>Sent: Thursday, February 11, 2016 8:56 AM
>>>Jon Elson wrote:
>>>We paid somewhere between 200 and 250K for our first 11/780. We had
>>>an RM05 and a TU77, and 256 KB of memory. It was a pretty basic
>>>system, but ran rings around the campus 360/65 system. We also had a
>>>pair of 370/145's that were an expensive joke. (The 360/65 ran rings
>>>around BOTH of them. They ran time sharing on them, limited to 4
>>>users/machine. We often had 8+ users plus batch jobs running on our
>>Any idea about the date of when VMS could do that with a VAX?
>From the very beginning? That is, 25 October 1977?
Since your answer seems to be an unstated question, I will attempt to
answer what you might have inferred. I was just attempting to note that
the CDC 3300 hardware was able to support that function more than a
DECADE earlier. By 1967 when I arrived, the system had already been
running for quite a while in support of many engineers who required access
to a computer that avoided the punch card route followed by submitting
the cards to the batch queue - and waiting - and waiting.
Access to an editor to compose the file followed by immediate placement
into the job queue was a huge improvement in the mid 1960s.
>VMS was built from the get-go as a timesharing operating system with a
>virtual memory architecture. It was not the best of such, nor was the
>hardware done particularly well (a VM system with no Page-Modified bit
>in hardware? seriously???), but it was certainly capable of handling
>that many users (and more, depending on job mix).
Agreed! But when you discuss the VAX and VMS, that is a decade later.
As long as the Cyber 3300 was able to get the job done in 1966, then a
quibble over implementation more than 10 years earlier seems a bit silly.
>So what was your question, really?
I did not have a question! You made your answer into a question
with your TWO question marks.
> Other timesharing systems existed, yes, but they were RPQ add-ons to
> standard batch-oriented hardware. Timesharing was built in on the PDP-6
> factory floor.
If by factory floor, you mean where the hardware was built, then based
on 55 years of developing programs, I disagree. "Timesharing", in my
opinion, is a result of the operating system software. For example,
RT-11 running on a PDP-11/73 (or faster CPU) is certainly NOT
designed to be a timesharing operating system, although under very
specific conditions it can operate in that manner. TSX-Plus will
execute on the identical hardware and have excellent performance
as a true timesharing operating system.
But the PDP-11 did not become the powerful computer that it
eventually became until at least about 1980. When RSTS/E was
combined with that level of hardware, it was able to support
timesharing as well. At this point when it is possible to run
RSTS/E on hardware that runs 100 times as fast as a PDP-11/93,
staying with RSTS/E makes sense for applications that are still
basically the same after 30 years.
So, back to my original statement which comments on much praising
of a VAX supporting editing sessions (along with running the programs
which were produced) around the mid 1970s. I doubt that the original
1.0 VMS handled timesharing very well. So I don't believe it was
unreasonable to make a statement that the same functions were available
more than a DECADE previously on a Cyber 3300 even though, as
you point out, the operating system in the mid 1960s was probably still
at the level of RT-11 as opposed to TSX-Plus.
I don't remember if the Cyber 3300 hardware even survived more than
10 years, but I suspect if it did, then by the mid 1970s it would have also
evolved into something that was much better than 10 years earlier.
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