Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!cis.ohio-state.edu!tut.cis.ohio-state.edu!ucbvax!agate!usenet.ins.cwru.edu!ncoast!allbery
From: allbery@NCoast.ORG (Brandon S. Allbery KF8NH)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: 8-bit death
Message-ID: <1991May12.180515.20191@NCoast.ORG>
Date: 12 May 91 18:05:15 GMT
References: <3335.tnews@templar.actrix.gen.nz> <1991May10.000135.7550@NCoast.ORG> <3636.tnews@templar.actrix.gen.nz>
Reply-To: allbery@ncoast.ORG (Brandon S. Allbery KF8NH)
Followup-To: comp.sys.amiga.advocacy
Organization: North Coast Public Access Un*x (ncoast)
Lines: 47

As quoted from <3636.tnews@templar.actrix.gen.nz> by jbickers@templar.actrix.gen.nz (John Bickers):
+---------------
| Quoted from <1991May10.000135.7550@NCoast.ORG> by allbery@NCoast.ORG (Brandon S. Allbery KB8JRR/AA):
| > As quoted from <3335.tnews@templar.actrix.gen.nz> by jbickers@templar.actrix.gen.nz (John Bickers):
| > |     PClone, it appears to involve using fixed tables of vectors into the
| > |     ROMs.
| >
| > ???  ONE interrupt is used for system calls --- INT 21H (that, by the way, is
| 
|     Then I must be including things akin to our external libraries. I'm
|     fairly sure that I've used a different number to do things with the
|     display. 0x10...?
+---------------

That's the BIOS viden interrupt.  As I said, you're "not supposed to do that".

+---------------
| > be dropped into place.  Theoretically, you're not supposed to call the BIOS
| > directly, but we all know what MS-Doesn't is like....
| 
|     Must be it. Now that I know so many microcomputer OSes do this sort
|     of thing, I'm certainly interested in _why_ they do it.
+---------------

Do *which* sort of thing?  One interrupt for the OS entry point?

That's probably because it potentially has even more possible values than you
have interrupts.  Should MS-Doesn't ever break the 256-syscall barrier (this
is, you understand, purely theoretical :-) , they can expand the system calls
to use AX instead of AL (set AH=0 and you have the original set), thus 65536
system calls.  That's probably the limit for DOS, though, until and unless
they drop 8088 "real" mode.  (Of course, AH is already used by some calls and
programmers expect AH to be unused in others, so the All-Holy Compatibility
with DOS 1.25 programs would be broken by this, so it'll never happen.  :-)

A better example:  a 680x0 Unix I used which used one of the "trap" calls and
placed the system call number in d0.  Now, how many possible system calls is
that?  4,294,967,296!  The Unix Thought Police will get them for kernel bloat
before they get anywhere near that many syscalls.  :-)  *How* many interrupts
did you say you had, in comparison (even using the Mac-noid 1010/1011 trap)?

++Brandon
-- 
Me: Brandon S. Allbery			  Ham: KF8NH on 10m,6m,2m,220,440,1.2
Internet: allbery@NCoast.ORG		       (restricted HF at present)
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