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From: gwyn@smoke.brl.mil (Doug Gwyn)
Newsgroups: comp.sys.apple2
Subject: Re: HLLs vs. Assembly
Message-ID: <15644@smoke.brl.mil>
Date: 30 Mar 91 15:12:35 GMT
References: <1991Mar28.012635.14869@nntp-server.caltech.edu> <13156@ucrmath.ucr.edu> <1991Mar30.080418.16299@ee.ualberta.ca>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 25

In article <1991Mar30.080418.16299@ee.ualberta.ca> jpenne@ee.ualberta.ca (Jerry Penner) writes:
>Portability.  It makes a lot more economic sense to write in a more
>portable language than in assembly.  I think this is the most
>important reason OS writers use C.

I think that's an argument for UNIX, but not in general.  Texas
Instruments, for example, wrote at least some of their OSes in
an extended version of Pascal; Burroughs wrote theirs in ESPOL,
which resembled Extended Algol; and DEC wrote VAX/VMS mainly in
Bliss, which is very analogous to C although different in detail.
In all these cases (UNIX also), an important consideration was
that it is simply easier to do a good job using a structured
high-level language.  The fact that there was negligible impact
on performance was of course crucial.

>I agree that using assembly is probably easier to write an OS in,
>because you don't have to fight the HLLs tendencies to constrict
>you into doing something in a certain way.

C was specifically designed to allow a high degree of exploitation
of the system architecture from within a structured high-level
language.  There are a few things that normally HAVE to be done in
assembly language, such as the glue between trap vectors and the C
code that processes the interrupts, but these are relatively few
and easily isolated.