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From: mohta@necom830.cc.titech.ac.jp (Masataka Ohta)
Newsgroups: comp.arch
Subject: Re: ACE (Was Re: Will NeXT survive?  Grow with the times?)
Message-ID: <168@titccy.cc.titech.ac.jp>
Date: 9 May 91 06:28:06 GMT
References: <21199@cbmvax.commodore.com> <3005@spim.mips.COM> <159@titccy.cc.titech.ac.jp> <3225@spim.mips.COM>
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In article <3225@spim.mips.COM> cprice@mips.com (Charlie Price) writes:

>The R4000 does the same sort of thing as the R3000A and the R6000.
>The *only* time the endian-ness of the processor is relevant is when
>a partial word (byte, half-word, triple) load or store is performed.

Then, shared memory between processes of different endian is impossible.

This means that access to a file through memory mapping mechanism is
impossible, if the file is accessed from processes of different endian.

But, it's OK to me, as I think mapped I/O is a bad idea.

>The only reasonable choice is to make character streams work correctly.

So, I said:

>>Thus, it is impossible to share memory (of byte stream) between binaries
                                          ^^^^^^^^^^^^^^

>The cost of doing the data transform for all I/O is not prohibitive.

Agreed. The cost is not so small, but, anyway, for disk I/O, the processor
must transfer data between user buffer and buffer cache.

>Supporting non-native endianness is clearly a compatibility measure
>and not the normal way to do business.

I hope so.

>1) To support programs from both the RISC/os (MIPS Computer Sys),
>   and SVR4 big-endian worlds and the Ultrix (DEC) and the
>   SCO (current and forthcoming OS) little-endian worlds.
>
>   Presumably as time goes by, machines based on the chip will all
>   become one endian (probably little) and one endianness will dominate
>   in the world of binaries.  The fringe applications will convert.

I really hope so.

But, don't forget that MIPS has been supporting both BSD and SysV and,
as time goes by, POSIX.

						Masataka Ohta