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From: terryl@sail.LABS.TEK.COM
Newsgroups: comp.unix.questions
Subject: Re: why different swapping modes on executables?
Message-ID: <9166@sail.LABS.TEK.COM>
Date: 20 Mar 91 18:53:31 GMT
References: <1991Mar12.012401.557@nowhere.uucp> <573@adpplz.UUCP> <1991Mar14.043302.3567@cbnewsk.att.com>
Reply-To: terryl@sail.LABS.TEK.COM
Distribution: na
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 23

In article <1991Mar14.043302.3567@cbnewsk.att.com> dyson@cbnewsk.att.com (john.s.dyson) writes:
>In article <573@adpplz.UUCP>, martin@adpplz.UUCP (Martin Golding) writes:
>> In <1991Mar12.104352.23097@kithrup.COM> sef@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!"
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