why different swapping modes on executables?

[terryl at sail.LABS.TEK.COM]

In article <1991Mar14.043302.3567 at cbnewsk.att.com> dyson at cbnewsk.att.com (john.s.dyson) writes:
>In article <573 at adpplz.UUCP>, martin at adpplz.UUCP (Martin Golding) writes:
>> In <1991Mar12.104352.23097 at kithrup.COM> sef at kithrup.COM (Sean Eric Fagan) 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.
>
>My memory is sometimes foggy, but I think that the magic number was
>the branch instruction around some header info in the a.out??????


     Pulling out my trusty (but VERY dusty!!! (-:) PDP11 Processor handbook,
the original a.out magic number 0407 (that's octal, folks!!!) says it is
an unconditional branch to seven words (i.e. 14 bytes) past the current PC;
thus, the original a.out magic number was chosen to branch around the a.out
header, since the header is 16 bytes long.....

__________________________________________________________
Terry Laskodi		"There's a permanent crease
     of			 in your right and wrong."
Tektronix		Sly and the Family Stone, "Stand!"
__________________________________________________________