Overlays - was Re: PDP-11 architecture Was: internet blocking problem ?

ANDY HOLT andy.holt at tesco.net
Fri Sep 11 11:31:17 CDT 2015

> ----- Original Message -----
> From: "Paul Koning" <paulkoning at comcast.net>
> To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>
> Sent: Friday, 11 September, 2015 4:58:41 PM

> I agree.  You can use overlays on any hardware platform that has random access secondary storage.  
> You need it if your programs are larger than your primary memory.  …

Overlays were also commonly used on Mag Tape systems before disk became common.

The George 1 and 2 operating systems for the ICL1900 series (and many compilers) came in
both disk overlaid and tape overlaid versions 
(e.g. the Fortran compiler XFAE was disk overlaid, XFAM was tape overlaid but otherwise
identical - both were designed for 16K word systems allowing about 3K for Exec and the "run-time"
overlay of George.)


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