[NTLUG:Discuss] Killing Off Linux: It's All Academic

[Steve Baker]

Eric Schnoebelen wrote:
> 
> Steve Baker writes:
> - I'm a little suprised when you say that V6 didn't have virtual memory.
> - That old PDP-11 only had 64K words of memory - 128Kbytes.  We often
> - had several people logged into it at once - it's hard to believe that
> - without virtual memory.
> 
>         It does (did?) have virtual memory, although not as we
> think of it now..  What V6 did was swap out entire programs when
> it needed to bring in another program and space wasn't
> available.  Additionally, processes were limited real memory
> (likely 32K words on your little PDP-11 above)

Oh - I see - so it paged physical memory - but not with virtual memory.

Hmmm - No MMU I guess.

I think our machine really did have 64k words of memory - there
was some hack on the 11/70 to have a 16 bit data address space
as well as a 16 bit code space.  I could be wrong about that though.

As an undergraduate, it was all rather amazing to be able to
actually interact with the machine.  In our first year, we did
all our programming with punched cards in a batch stream with
a 1 hour turn-around.  It made you a LOT more careful about
typo's!

Compared to that, UNIX was like magic.  The UNIX machine was
chronically short of hard disk space - so we dumped our entire
workspace to DEC-tape at the end of every session - and restored
it again at the start of the next one.  DEC-tapes were really
neat storage devices. Fast and *nearly* as portable as floppies.

We had a PDP-11/20 too - we used it for learning to write OS's
and device drivers.  It was a totally "bare" machine. No boot
ROM, no OS, no hard drive.  You had to key in a paper tape loader
from the front panel switches to get your code loaded.  Between
those two PDP-11's I learned more practical programming than
in all of the lectures in 3 years of my degree course. Played
a lot of core-wars on the 11/20 too!

-- 
Steve Baker                  http://web2.airmail.net/sjbaker1
sjbaker1 at airmail.net (home)  http://www.woodsoup.org/~sbaker
sjbaker at hti.com      (work)