VAXen and minimal memory (was Re: The PDP11/04 has landed..)

Rich Alderson RichA at
Thu Feb 11 13:48:08 CST 2016

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 
>> 780.) 

> Any idea about the date of when VMS could do that with a VAX?

From the very beginning?  That is, 25 October 1977?

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).

DEC was the first company to build timeshared large systems as standard[1],
beginning with the PDP-6.  The PDP-10 (a reimplementation of the PDP-6) was
successful enough to go through 3 generations (renamed to DECsystem-10 and
DECSYSTEM-20) of market success, enough to inspire 2 research labs (Xerox
PARC and Stanford Artificial Intelligence Laboratory) and 3 manufacturers
(Foonly, Systems Concepts, and XKL) to design and, except for SAIL[2], to
build clones.  The PDP-6 came out in 1964, the PDP-10 in 1967 (KA-10), with
later members of the family in 1971 (KI-10), 1974 (KL-10), and 1979 (KS-10).
All of them were capable of handling up to 100 users.

So what was your question, really?


[1] 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.

[2] DEC liked the design of the SAIL machine so much that they bought it,
    and hired the grad student who maintained the CAD software written at
    SAIL which was used to design it.  That became the 3rd generation of the
    PDP-10 family, the KL-10 processor.

Rich Alderson
Vintage Computing Sr. Systems Engineer
Living Computer Museum
2245 1st Avenue S
Seattle, WA 98134

mailto:RichA at

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