Re: Address bits again, Article on new mainframe use

It appears that Lawrence D'Oliveiro  <ldo@nz.invalid> said:

It is true that, while the x86 segmentation system sucked, the PDP-11’s
address limitations made it look good by comparison.

I don't think anyone at DEC thought it was an expansion mechanism.  The 11/45 and /70
had eight 8K pages in each address space of which there were six, two each for
user, supervisor, and kernel.  I think they thought it was paging, but of course
8K pages were way too large.  So they overreacted and the Vax pages were 512 bytes
which were too small.

VAX stood for Virtual Address Extension.  The key improvement was the 32
bit addresses.  Everything else was a detail.

>
Hey, don’t forget the kitchen-sink instruction set. ;)

We can try to forget, but it's hard.

Also don't forget that back in that era everyone who had disks used
overlays.

>
Or multiple passes, as separate executables. One of our lecturers got hold
of a copy of a Pascal compiler for our PDP-11. That consisted of two
separate programs, and it wasn’t quite a complete Pascal implementation. ...

Good point.  The dmr C compiler was four passes, a front end that turned source
code into trees, a code generator that wrote assembler, an optional optimizer
that rewrote the assembler, and the assembler which created the object file,
Each pass was a separate program.

The IBM mainframe linkers had complicated ways to build
overlays and squeeze programs into 64K or whatever. ...

I never quite learned how to build overlaid programs. ...

When I was working on the DOS version of Javelin we used a linker that had overlays
just like the mainframe linkers.  I got it to work and squeezed the code into
about 1/3 the space it'd take otherwise but it wasn't pleasant.

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