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Comment by Alex63 | Hacker News Reader

That takes me back. My first job as a programmer after university was on a PDP-11/78, on RSTS/E. I don't miss overlays!

Overlays on 8" floppies, the whirr-kerchunk of retries has left a scar across my soul.

This brings back great memories.

UCSD Pascal, TECO/KED, learning Dibol.... I learned on an 11/23 running RT-11, VT100, dual RL02s (oh, yeah). I never did learn anything serious about the O/S.

Our high school had an ancient PDP-8 we used DEC Basic on.

KED on a VT100 under RT-11 was awesome (compared to everyhing else at the time). The right-hand finger-dance across PF1-PF4 felt so natural, and despite it being at 9600 baud it never felt slow.

Awhile back, I was playing with 2.11BSD for the PDP-11 in simh and was trying to learn PDP-11 assembly. I would read things about overlays, but I could never find a resource to learn more about them. Were there any manuals or textbooks which gave good coverage to overlays?

Overlays (at least in RT-11) are just chunks of code that would load at a specific address in memory. So if your program didn't fit into memory, a good chunk of it could run in an overlay area.

So for example your code could have an always-resident portion say from 0 to 100000 octal (the lowest half of memory) and an overlay area from 100000 to 140000. We had a program that has an input, calculation and runtime phase so it suited the overlay model; programs that needed all their code in memory at the same time by comparison would not be suited to overlays (especially on 8" floppies, where loading an overlay was accompanied by plenty of mechanical noise).

There are a lot of things I don't miss! x86 segmented architecture, for example. Even modern embedded programming on an ARM Cortex-M feels luxurious compared to not that long ago.

It's almost embarrassing to tell young graduates about unreal mode and triple fault.

Yep, which is somehow funny to see people discussing what you can or cannot do on ESP286 and ESP32, when compared with CP/M and MS-DOS early hardware, they are server class.

It could always be worse. As I remember it, MS-DOS also had overlays....

Yep, Turbo Pascal 3.0 supported them.

And you could also use tricks like TSR for simulating multiprocessing.

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