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(web2c.info)Hardware and memory dumps

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Hardware and memory dumps
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  By default, memory dump files are generally sharable between
architectures of different types; specifically, on machines of different
endianness (Note: Byte order.).  (This is a feature
of the Web2c implementation, and is not true of all TeX
implementations.)  If you specify `--disable-dump-share' to
`configure', however, memory dumps will be endian-dependent.

  The reason to do this is speed.  To achieve endian-independence, the
reading of memory dumps on LittleEndian architectures, such as PC's and
DEC architectures, is somewhat slowed (all the multibyte values have to
be swapped).  Usually, this is not noticeable, and the advantage of
being able to share memory dumps across all platforms at a site far
outweighs the speed loss.  But if you're installing Web2c for use on
LittleEndian machines only, perhaps on a PC being used only by you, you
may wish to get maximum speed.

  TeXnically, even without `--disable-dump-share', sharing of `.fmt'
files cannot be guaranteed to work.  Floating-point values are always
written in native format, and hence will generally not be readable
across platforms.  Fortunately, TeX uses floating point only to
represent glue ratios, and all common formats (plain, LaTeX, AMSTeX,
...) do not do any glue setting at `.fmt'-creation time.  Metafont and
MetaPost do not use floating point in any dumped value at all.

  Incidentally, different memory dump files will never compare equal
byte-for-byte, because the program always dumps the current date and
time. So don't be alarmed by just a few bytes difference.

  If you don't know what endianness your machine is, and you're curious,
here is a little C program to tell you. (The `configure' script
contains a similar program.)  This is from the book `C: A Reference
Manual', by Samuel P. Harbison and Guy L. Steele Jr. (Note:
References).

     main ()
     {
       /* Are we little or big endian?  From Harbison&Steele.  */
       union
       {
         long l;
         char c[sizeof (long)];
       } u;
       u.l = 1;
       if (u.c[0] == 1)
         printf ("LittleEndian\n");
       else if (u.c[sizeof (long) - 1] == 1)
         printf ("BigEndian\n");
       else
         printf ("unknownEndian");
     
       exit (u.c[sizeof (long) - 1] == 1);
     }