Document wide integers better.

* buffers.texi (Buffers):
* files.texi (Visiting): Default buffer maximum is now 2 EiB typically.

doc/emacs/ChangeLog

@@ -1,3 +1,9 @@
+2011-06-02  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Document wide integers better.
+	* buffers.texi (Buffers):
+	* files.texi (Visiting): Default buffer maximum is now 2 EiB typically.
+
 2011-05-28  Chong Yidong  <cyd@stupidchicken.com>
 
 	* custom.texi (Hooks): Reorganize.  Mention Prog mode.

doc/emacs/buffers.texi

@@ -43,8 +43,11 @@ can be different from the value in other buffers.  @xref{Locals}.
   A buffer's size cannot be larger than some maximum, which is defined
 by the largest buffer position representable by the @dfn{Emacs
 integer} data type.  This is because Emacs tracks buffer positions
-using that data type.  For 32-bit machines, the largest buffer size is
-512 megabytes.
+using that data type.  For most machines, the maximum buffer size
+enforced by the data types is @math{2^61 - 2} bytes, or about 2 EiB.
+For some older machines, the maximum is @math{2^29 - 2} bytes, or
+about 512 MiB.  Buffer sizes are also limited by the size of Emacs's
+virtual memory.
 
 @menu
 * Select Buffer::       Creating a new buffer or reselecting an old one.

doc/emacs/files.texi

@@ -209,7 +209,8 @@ to reread it.
 about 10 megabytes), Emacs asks you for confirmation first.  You can
 answer @kbd{y} to proceed with visiting the file.  Note, however, that
 Emacs cannot visit files that are larger than the maximum Emacs buffer
-size, which is around 512 megabytes on 32-bit machines
+size, which is limited by the amount of memory Emacs can allocate
+and by the integers that Emacs can represent
 (@pxref{Buffers}).  If you try, Emacs will display an error message
 saying that the maximum buffer size has been exceeded.