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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.unix.wizards
Subject: Re: multiple-machine executables for Suns?
Message-ID: <24830@sun.uucp>
Date: Tue, 4-Aug-87 14:20:04 EDT
Article-I.D.: sun.24830
Posted: Tue Aug  4 14:20:04 1987
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> Sun-2 binaries will work on a Sun-3, but not vice-versa and I expect that
> Sun-4 binaries work iff they're on a Sun-4.

Since the SPARC instruction set does not at all resemble the 68K instruction
set, this is certainly true.

> I asked someone at Sun about this and they said that although Sun had talked
> about it there were no plans for doing it at the current time.  As the only
> specific reason for not doing this, he cited the extra disk space required
> for such a format.

Which, in our case, is an excellent reason.  SunOS releases are, for
better or worse, quite big; were the standard binaries to contain
several types of image, you might have to cut back quite a bit on
optional software to fit it on a 71MB shoebox (or might not be able
to fit it at all).

Also note that, if the standard development environment were to build
3-way executables, this environment would have to contain both 68K
and SPARC compilers, as well as 68K and SPARC libraries (or even
68010, 68020, and SPARC libraries).

In addition, were you to have a server serving several different Sun
*and* non-Sun architectures (as will be possible once ND is
eliminated), you'd either have to teach all the non-Sun machines
about this executable format and stuff the additional images into the
common image, or use the idea only for Suns.

> Here, disk space is much cheaper than programmer time and I'd gladly have
> binaries that are twice as big if I didn't have to worry about two
> different executables.

I'm not sure what the problem is.  If you have several different
kinds of executables, you have to compile the program N times, once
for each kind of machine.  If you have multiple-machine executables,
you have to compile the program N times, once for each kind of
machine.  Both of these will take up some amount of programmer time.

There is some additional maintenance time for installing the various
different forms of executable image.  I don't see why this is a major
component of the total development time, though.

> In some ways the current incompatibilities help Sun -- they provides some
> motivation to roll out Sun-2s and roll in Sun-3s,

That was NOT the intent.  If you can build Sun-2 binaries, you can
run them on Sun-3s; we now offer cross-compilers, so you can build
Sun-2 and Sun-3 binaries on Sun-3s.  (There is a charge for these;
please do not attempt to engage me in a debate about whether this is
the right thing to do or not, because 1) I don't have sufficient
information about *all* sides of the question to have an
authoritative opinion and 2) I don't make policy on that anyway, so
if you don't like it you're better off complaining to your
salesperson.  My *personal* opinion is that we shouldn't charge for
it, but there may be a good reason for doing so that I don't know
about.)

> but on the other hand, it lessens (to near-zero for me) the motivation to
> roll in a Sun-4.

I still don't see what the executable image format has to do with
this; there will be customers to whom binary compatibility with
Sun-2s and Sun-3s is more important than the added performance of a
Sun-4, so they will buy Sun-3s instead of Sun-4s.  The Sun-4 is aimed
at customers to whom the expense of recompiling their software (and,
if necessary, changing their code to "play by the rules" of portable
C) is more than offset by the benefits of the added performance of
the Sun-4.

DISCLAIMER for the less-bright members of the audience: none of this
represents the official opinion of Sun Microsystems, it merely
represents my understanding of some of the issues involved (but then
one hopes most of the audience understood that anyway).
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com