why different swapping modes on executables?

[Doug Gwyn]

In article <573 at adpplz.UUCP> martin at adpplz.UUCP (Martin Golding) writes:
>My impression is that the (original) version of the Magic Number was
>the actual value to load into the PDP 11 MMU control register, to select
>one or the other model.

No, not at all.

The original a.out magic number was a PDP-11 branch-always instruction
that jumped around the a.out header, so an a.out could be executed
directly, as in a boot block or standalone diagnostic program.