[TUHS] [Bulk] PDP-11 questions

Mark Green markwgreen at rogers.com
Mon Jan 25 04:06:40 AEST 2016

Whether a PDP11 came with an operating system depended upon how it was purchased, none of the ones that I bought came with an OS.  The PDP11/20 was early in the line, so it may have come with some form of OS.

DRAM on a PDP11/20??  You've got your decades mixed up.  DRAM came much later than the PDP11 architecture.  The PDP11/20 used core memory, no need for initialization.  Core is non-volatile, so it maintained its contents when power was removed.  It was common to keep whatever software you were using in memory, so when you came back you just turned on the power and continued from where you were.  One of the groups that I worked with used to keep all their software libraries on core boards, they would switch the boards between computers between computers whenever they needed to library.

All the early PDP11s had full consoles, so a boot loader could be entered through the console.  There were ROM boards that had some of the common bootstraps.

There were desktop PDP11s, depending upon what you mean by a desktop.  Healthkit produced a low end PDP11 system for hobbyists that would be considered to be a desktop.  DEC was slow getting into that area, there were some desktop like PDP11 systems produced near the end of the architecture, but DEC desktops really didn't appear until the VAX and MIPS era.

-----Original Message-----
From: TUHS [mailto:tuhs-bounces at minnie.tuhs.org] On Behalf Of Mark Longridge
Sent: January 24, 2016 12:37 PM
To: tuhs <tuhs at minnie.tuhs.org>
Subject: [Bulk] [TUHS] PDP-11 questions

Ok, I got a few questions about PDP-11.

First, I was wondering when Bell Labs got that first PDP-11/20 what software (if any) came with it? I assume when one bought a PDP-11/20 you would get some type of OS with it.

According to the folks at alt.sys.pdp11 the PDP-11 computer doesn't have anything equivalent to a PC's BIOS. But I know a bit about what a PC's BIOS does and that includes RAM Initialization. Wouldn't the DRAM on the PDP-11/something need to be initialized too? Perhaps an older
PDP-11 doesn't have DRAM but surely the later models did?

Now the last question has to do with what made the PDP-11 architecture so great. Part of that had to be the relatively affordablility of the
PDP-11 and of course it was the machine that made Unix possible. It seems though that there should have been a PDP-11 based desktop and as far as I can tell that didn't happen. Instead we got a bunch of micros with 8080, z80 and 6502 cpus, but nothing that could run Unix, at least not a Unix v7 with source code.


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