elisp: Disabling Multibyte
32.2 Disabling Multibyte Characters
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By default, Emacs starts in multibyte mode: it stores the contents of
buffers and strings using an internal encoding that represents non-ASCII
characters using multi-byte sequences. Multibyte mode allows you to use
all the supported languages and scripts without limitations.
Under very special circumstances, you may want to disable multibyte
character support, for a specific buffer. When multibyte characters are
disabled in a buffer, we call that “unibyte mode”. In unibyte mode,
each character in the buffer has a character code ranging from 0 through
255 (0377 octal); 0 through 127 (0177 octal) represent ASCII characters,
and 128 (0200 octal) through 255 (0377 octal) represent non-ASCII
characters.
To edit a particular file in unibyte representation, visit it using
‘find-file-literally’. 
Visiting Functions. You can convert a
multibyte buffer to unibyte by saving it to a file, killing the buffer,
and visiting the file again with ‘find-file-literally’. Alternatively,
you can use ‘C-x <RET> c’ (‘universal-coding-system-argument’) and
specify ‘raw-text’ as the coding system with which to visit or save a
file. Specifying a Coding System for File Text (emacs)Text
Coding. Unlike ‘find-file-literally’, finding a file as ‘raw-text’
doesn’t disable format conversion, uncompression, or auto mode
selection.
The buffer-local variable ‘enable-multibyte-characters’ is non-‘nil’
in multibyte buffers, and ‘nil’ in unibyte ones. The mode line also
indicates whether a buffer is multibyte or not. With a graphical
display, in a multibyte buffer, the portion of the mode line that
indicates the character set has a tooltip that (amongst other things)
says that the buffer is multibyte. In a unibyte buffer, the character
set indicator is absent. Thus, in a unibyte buffer (when using a
graphical display) there is normally nothing before the indication of
the visited file’s end-of-line convention (colon, backslash, etc.),
unless you are using an input method.
You can turn off multibyte support in a specific buffer by invoking
the command ‘toggle-enable-multibyte-characters’ in that buffer.
Info Catalog
elisp: Text Representations
elisp: Non-ASCII Characters
elisp: Converting Representations