@c This is part of the Emacs manual. @c Copyright (C) 1985, 86, 87, 93, 94, 95, 1997 Free Software Foundation, Inc. @c See file emacs.texi for copying conditions. @node MS-DOS, Manifesto, Antinews, Top @appendix Emacs and MS-DOS @cindex MS-DOG @cindex MS-DOS peculiarities This section briefly describes the peculiarities of using Emacs under the MS-DOS ``operating system'' (also known as ``MS-DOG''). If you build Emacs for MS-DOS, the binary will also run on Windows 3.X, Windows NT, Windows 9X, or OS/2 as a DOS application; the information in this chapter applies for all of those systems, if you use an Emacs that was built for MS-DOS. Note that it is possible to build Emacs specifically for Windows NT or Windows 9X. If you do that, most of this chapter does not apply; instead, you get behavior much closer to what is documented in the rest of the manual, including support for long file names, multiple frames, scroll bars, mouse menus, and subprocesses. However, the section on text files and binary files does still apply. There are also two sections at the end of this chapter which apply specifically for Windows NT and 9X. @menu * Input: MS-DOS Input. Keyboard and mouse usage on MS-DOS. * Display: MS-DOS Display. Fonts, frames and display size on MS-DOS. * Files: MS-DOS File Names. File name conventions on MS-DOS. * Text and Binary:: Text files on MS-DOS use CRLF to separate lines. * Printing: MS-DOS Printing. How to specify the printer on MS-DOS. * I18N: MS-DOS and MULE. Support for internationalization on MS-DOS. * Processes: MS-DOS Processes. Running subprocesses on MS-DOS. * Windows Processes:: Running subprocesses on Windows. * Windows System Menu:: Controlling what the ALT key does. @end menu @node MS-DOS Input @section Keyboard and Mouse on MS-DOS @cindex Meta (under MS-DOS) @cindex Hyper (under MS-DOS) @cindex Super (under MS-DOS) @vindex dos-super-key @vindex dos-hyper-key The PC keyboard maps use the left @key{ALT} key as the @key{META} key. You have two choices for emulating the @key{SUPER} and @key{HYPER} keys: choose either the right @key{CTRL} key or the right @key{ALT} key by setting the variables @code{dos-hyper-key} and @code{dos-super-key} to 1 or 2 respectively. If neither @code{dos-super-key} nor @code{dos-hyper-key} is 1, then by default the right @key{ALT} key is also mapped to the @key{META} key. However, if the MS-DOS international keyboard support program @file{KEYB.COM} is installed, Emacs will @emph{not} map the right @key{ALT} to @key{META}, since it is used for accessing characters like @kbd{~} and @kbd{@@} on non-US keyboard layouts; in this case, you may only use the left @key{ALT} as @key{META} key. @kindex C-j @r{(MS-DOS)} @vindex dos-keypad-mode The variable @code{dos-keypad-mode} is a flag variable that controls what key codes are returned by keys in the numeric keypad. You can also define the keypad @key{ENTER} key to act like @kbd{C-j}, by putting the following line into your @file{_emacs} file: @smallexample ;; Make the Enter key from the Numeric keypad act as C-j. (define-key function-key-map [kp-enter] [?\C-j]) @end smallexample @kindex DEL @r{(MS-DOS)} @kindex BS @r{(MS-DOS)} The key that is called @key{DEL} in Emacs (because that's how it is designated on most workstations) is known as @key{BS} (backspace) on a PC. That is why the PC-specific terminal initialization remaps the @key{BS} key to act as @key{DEL}; the @key{DEL} key is remapped to act as @kbd{C-d} for the same reasons. @kindex C-g @r{(MS-DOS)} @kindex C-BREAK @r{(MS-DOS)} @cindex quitting on MS-DOS Emacs built for MS-DOS recognizes @kbd{C-@key{BREAK}} as a quit character, just like @kbd{C-g}. This is because Emacs cannot detect that you have typed @kbd{C-g} until it is ready for more input. As a consequence, you cannot use @kbd{C-g} to stop a running command (@pxref{Quitting}). By contrast, @kbd{C-@key{BREAK}} @emph{is} detected as soon as you type it (as @kbd{C-g} is on other systems), so it can be used to stop a running command and for emergency escape (@pxref{Emergency Escape}). @cindex mouse support under MS-DOS Emacs on MS-DOS supports a mouse (on the default terminal only). The mouse commands work as documented, including those that use menus and the menu bar (@pxref{Menu Bar}). Scroll bars don't work in MS-DOS Emacs. PC mice usually have only two buttons; these act as @kbd{Mouse-1} and @kbd{Mouse-2}, but if you press both of them together, that has the effect of @kbd{Mouse-3}. @cindex Windows clipboard support Emacs built for MS-DOS supports clipboard operations when it runs on Windows. Commands that put text on the kill ring, or yank text from the ring, check the Windows clipboard first, just as Emacs does on X Windows (@pxref{Mouse Commands}). Only the primary selection and the cut buffer are supported by MS-DOS Emacs on Windows; the secondary selection always appears as empty. Due to the way clipboard access is implemented by Windows, the length of text you can put into the clipboard is limited by the amount of free DOS memory that is available to Emacs. Usually, up to 620KB of text can be put into the clipboard, but this limit depends on the system configuration and is lower if you run Emacs as a subprocess of another program. If the killed text does not fit, Emacs prints a message saying so, and does not put the text into the clipboard. Null characters also cannot be put into the Windows clipboard. If the killed text includes null characters, Emacs does not put such text into the clipboard, and prints in the echo area a message to that effect. @vindex dos-display-scancodes The variable @code{dos-display-scancodes}, when non-@code{nil}, directs Emacs to display the ASCII value and the keyboard scan code of each keystroke; this feature serves as a complement to the @code{view-lossage} command, for debugging. @node MS-DOS Display @section Display on MS-DOS @cindex faces under MS-DOS @cindex fonts, emulating under MS-DOS Display on MS-DOS cannot use font variants, like bold or italic, but it does support multiple faces, each of which can specify a foreground and a background color. Therefore, you can get the full functionality of Emacs packages that use fonts (such as @code{font-lock}, Enriched Text mode, and others) by defining the relevant faces to use different colors. Use the @code{list-colors-display} command (@pxref{Frame Parameters}) and the @code{list-faces-display} command (@pxref{Faces}) to see what colors and faces are available and what they look like. The section @ref{MS-DOS and MULE}, later in this chapter, describes how Emacs displays glyphs and characters which aren't supported by the native font built into the DOS display. @cindex frames on MS-DOS Multiple frames (@pxref{Frames}) are supported on MS-DOS, but they all overlap, so you only see a single frame at any given moment. That single visible frame occupies the entire screen. When you run Emacs from MS-Windows DOS box, you can make the visible frame smaller than the full screen, but Emacs still cannot display more than a single frame at a time. @cindex frame size under MS-DOS @findex mode4350 @findex mode25 The @code{mode4350} command switches the display to 43 or 50 lines, depending on your hardware; the @code{mode25} command switches to the default 80x25 screen size. By default, Emacs only knows how to set screen sizes of 80 columns by 25, 28, 35, 40, 43 or 50 rows. However, if your video adapter has special video modes that will switch the display to other sizes, you can have Emacs support those too. When you ask Emacs to switch the frame to @var{n} rows by @var{m} columns dimensions, it checks if there is a variable called @code{screen-dimensions-@var{n}x@var{m}}, and if so, uses its value (which must be an integer) as the video mode to switch to. (Emacs switches to that video mode by calling the BIOS @code{Set Video Mode} function with the value of @code{screen-dimensions-@var{n}x@var{m}} in the @code{AL} register.) For example, suppose your adapter will switch to 66x80 dimensions when put into video mode 85. Then you can make Emacs support this screen size by putting the following into your @file{_emacs} file: @example (setq screen-dimensions-66x80 85) @end example Since Emacs on MS-DOS can only set the frame size to specific supported dimensions, it cannot honor every possible frame resizing request. When an unsupported size is requested, Emacs chooses the next larger supported size beyond the specified size. For example, if you ask for 36x80 frame, you will get 40x80 instead. The variables @code{screen-dimensions-@var{n}x@var{m}} are used only when they exactly match the specified size; the search for the next larger supported size ignores them. In the above example, even if your VGA supports 38x80 dimensions and you define a variable @code{screen-dimensions-38x80} with a suitable value, you will still get 40x80 screen when you ask for a 36x80 frame. If you want to get the 38x80 size in this case, you can do it by setting the variable named @code{screen-dimensions-36x80} with the same video mode value as @code{screen-dimensions-38x80}. Changing frame dimensions on MS-DOS has the effect of changing all the other frames to the new dimensions. @node MS-DOS File Names @section File Names on MS-DOS @cindex file names under MS-DOS @cindex init file, default name under MS-DOS MS-DOS normally uses a backslash, @samp{\}, to separate name units within a file name, instead of the slash used on other systems. Emacs on MS-DOS permits use of either slash or backslash, and also knows about drive letters in file names. On MS-DOS, file names are case-insensitive and limited to eight characters, plus optionally a period and three more characters. Emacs knows enough about these limitations to handle file names that were meant for other operating systems. For instance, leading dots @samp{.} in file names are invalid in MS-DOS, so Emacs transparently converts them to underscores @samp{_}; thus your default init file (@pxref{Init File}) is called @file{_emacs} on MS-DOS. Excess characters before or after the period are generally ignored by MS-DOS itself; thus, if you visit the file @file{LongFileName.EvenLongerExtension}, you will silently get @file{longfile.eve}, but Emacs will still display the long file name on the mode line. Other than that, it's up to you to specify file names which are valid under MS-DOS; the transparent conversion as described above only works on file names built into Emacs. @cindex backup file names on MS-DOS The above restrictions on the file names on MS-DOS make it almost impossible to construct the name of a backup file (@pxref{Backup Names}) without losing some of the original file name characters. For example, the name of a backup file for @file{docs.txt} is @file{docs.tx~} even if single backup is used. @cindex file names under Windows 95/NT @cindex long file names in DOS box under Windows 95/NT If you run Emacs as a DOS application under Windows 9X, you can turn on support for long file names. If you do that, Emacs doesn't truncate file names or convert them to lower case; instead, it uses the file names that you specify, verbatim. To enable long file name support, set the environment variable @code{LFN} to @samp{y} before starting Emacs. Unfortunately, Windows NT doesn't allow DOS programs to access long file names, so Emacs built for MS-DOS will only see their short 8+3 aliases. @cindex @code{HOME} directory under MS-DOS MS-DOS has no notion of home directory, so Emacs on MS-DOS pretends that the directory where it is installed is the value of @code{HOME} environment variable. That is, if your Emacs binary, @file{emacs.exe}, is in the directory @file{c:/utils/emacs/bin}, then Emacs acts as if @code{HOME} were set to @samp{c:/utils/emacs}. In particular, that is where Emacs looks for the init file @file{_emacs}. With this in mind, you can use @samp{~} in file names as an alias for the home directory, as you would in Unix. You can also set @code{HOME} variable in the environment before starting Emacs; its value will then override the above default behavior. Emacs on MS-DOS handles the directory name @file{/dev} specially, because of a feature in the emulator libraries of DJGPP that pretends I/O devices have names in that directory. We recommend that you avoid using an actual directory named @file{/dev} on any disk. @node Text and Binary @section Text Files and Binary Files @cindex text and binary files on MS-DOS/MS-Windows GNU Emacs uses newline characters to separate text lines. This is the convention used on Unix, on which GNU Emacs was developed, and on GNU systems since they are modeled on Unix. @cindex end-of-line conversion on MS-DOS/MS-Windows MS-DOS and MS-Windows normally use carriage-return linefeed, a two-character sequence, to separate text lines. (Linefeed is the same character as newline.) Therefore, convenient editing of typical files with Emacs requires conversion of these end-of-line (EOL) sequences. And that is what Emacs normally does: it converts carriage-return linefeed into newline when reading files, and converts newline into carriage-return linefeed when writing files. The same mechanism that handles conversion of international character codes does this conversion also (@pxref{Coding Systems}). @cindex cursor location, under MS-DOS @cindex point location, under MS-DOS One consequence of this special format-conversion of most files is that character positions as reported by Emacs (@pxref{Position Info}) do not agree with the file size information known to the operating system. @vindex file-name-buffer-file-type-alist Some kinds of files should not be converted, because their contents are not really text. Therefore, Emacs on MS-DOS distinguishes certain files as @dfn{binary files}, and reads and writes them verbatim. (This distinction is not part of MS-DOS; it is made by Emacs only.) These include executable programs, compressed archives, etc. Emacs uses the file name to decide whether to treat a file as binary: the variable @code{file-name-buffer-file-type-alist} defines the file-name patterns that indicate binary files. Note that if a file name matches one of the patterns for binary files in @code{file-name-buffer-file-type-alist}, Emacs uses the @code{no-conversion} coding system (@pxref{Coding Systems}) which turns off @emph{all} coding-system conversions, not only the EOL conversion. In addition, if Emacs recognizes from a file's contents that it uses newline rather than carriage-return linefeed as its line separator, it does not perform conversion when reading or writing that file. Thus, you can read and edit files from Unix or GNU systems on MS-DOS with no special effort, and they will be left with their Unix-style EOLs. @findex find-file-text @findex find-file-binary You can visit a file and specify whether to treat a file as text or binary using the commands @code{find-file-text} and @code{find-file-binary}. End-of-line conversion is part of the general coding system conversion mechanism, so another way to control whether to treat a file as text or binary is with the commands for specifying a coding system (@pxref{Specify Coding}). For example, @kbd{C-x @key{RET} c undecided-unix @key{RET} C-x C-f foobar.txt} visits the file @file{foobar.txt} without converting the EOLs. The mode line indicates whether end-of-line translation was used for the current buffer. Normally a colon appears after the coding system letter near the beginning of the mode line. If MS-DOS end-of-line translation is in use for the buffer, this character changes to a backslash. @cindex untranslated file system @findex add-untranslated-filesystem When you use NFS or Samba to access file systems that reside on computers using Unix or GNU systems, Emacs should not perform end-of-line translation on any files in these file systems--not even when you create a new file. To request this, designate these file systems as @dfn{untranslated} file systems by calling the function @code{add-untranslated-filesystem}. It takes one argument: the file system name, including a drive letter and optionally a directory. For example, @example (add-untranslated-filesystem "Z:") @end example @noindent designates drive Z as an untranslated file system, and @example (add-untranslated-filesystem "Z:\\foo") @end example @noindent designates directory @file{\foo} on drive Z as an untranslated file system. Most often you would use @code{add-untranslated-filesystem} in your @file{_emacs} file, or in @file{site-start.el} so that all the users at your site get the benefit of it. @findex remove-untranslated-filesystem To countermand the effect of @code{add-untranslated-filesystem}, use the function @code{remove-untranslated-filesystem}. This function takes one argument, which should be a string just like the one that was used previously with @code{add-untranslated-filesystem}. @node MS-DOS Printing @section Printing and MS-DOS Printing commands, such as @code{lpr-buffer} (@pxref{Hardcopy}) and @code{ps-print-buffer} (@pxref{Postscript}) can work in MS-DOS and MS-Windows by sending the output to one of the printer ports, if a Unix-style @code{lpr} program is unavailable. This behaviour is controlled by the same variables that control printing with @code{lpr} on Unix (@pxref{Hardcopy}, @pxref{Postscript Variables}), but the defaults for these variables on MS-DOS and MS-Windows are not the same as the defaults on Unix. @vindex printer-name @r{(MS-DOS)} If you want to use your local printer, printing on it in the usual DOS manner, then set the Lisp variable @code{lpr-command} to @code{""} (its default value) and @code{printer-name} to the name of the printer port---for example, @code{"PRN"}, the usual local printer port (that's the default), or @code{"LPT2"}, or @code{"COM1"} for a serial printer. You can also set @code{printer-name} to a file name, in which case ``printed'' output is actually appended to that file. If you set @code{printer-name} to @code{"NUL"}, printed output is silently discarded (sent to the system null device). On MS-Windows, when the Windows network software is installed, you can also use a printer shared by another machine by setting @code{printer-name} to the UNC share name for that printer--for example, @code{"//joes_pc/hp4si"}. (It doesn't matter whether you use forward slashes or backslashes here.) To find out the names of shared printers, run the command @samp{net view} at a DOS command prompt to obtain a list of servers, and @samp{net view @var{server-name}} to see the names of printers (and directories) shared by that server. If you set @code{printer-name} to a file name, it's best to use an absolute file name. Emacs changes the working directory according to the default directory of the current buffer, so if the file name in @code{printer-name} is relative, you will end up with several such files, each one in the directory of the buffer from which the printing was done. @findex print-buffer @r{(MS-DOS)} @findex print-region @r{(MS-DOS)} @vindex lpr-headers-switches @r{(MS-DOS)} The commands @code{print-buffer} and @code{print-region} call the @code{pr} program, or use special switches to the @code{lpr} program, to produce headers on each printed page. MS-DOS and MS-Windows don't normally have these programs, so by default, the variable @code{lpr-headers-switches} is set so that the requests to print page headers are silently ignored. Thus, @code{print-buffer} and @code{print-region} produce the same output as @code{lpr-buffer} and @code{lpr-region}, respectively. If you do have a suitable @code{pr} program (for example, from GNU Textutils), set @code{lpr-headers-switches} to @code{nil}; Emacs will then call @code{pr} to produce the page headers, and print the resulting output as specified by @code{printer-name}. @vindex print-region-function @r{(MS-DOS)} @cindex lpr usage under MS-DOS @vindex lpr-command @r{(MS-DOS)} @vindex lpr-switches @r{(MS-DOS)} Finally, if you do have an @code{lpr} work-alike, you can set the variable @code{lpr-command} to @code{"lpr"}. Then Emacs will use @code{lpr} for printing, as on other systems. (If the name of the program isn't @code{lpr}, set @code{lpr-command} to specify where to find it.) The variable @code{lpr-switches} has its standard meaning when @code{lpr-command} is not @code{""}. If the variable @code{printer-name} has a string value, it is used as the value for the @code{-P} option to @code{lpr}, as on Unix. @findex ps-print-buffer @r{(MS-DOS)} @findex ps-spool-buffer @r{(MS-DOS)} @vindex ps-printer-name @r{(MS-DOS)} @vindex ps-lpr-command @r{(MS-DOS)} @vindex ps-lpr-switches @r{(MS-DOS)} A parallel set of variables, @code{ps-lpr-command}, @code{ps-lpr-switches}, and @code{ps-printer-name} (@pxref{Postscript Variables}), defines how PostScript files should be printed. These variables are used in the same way as the corresponding variables described above for non-PostScript printing. Thus, the value of @code{ps-printer-name} is used as the name of the device (or file) to which PostScript output is sent, just as @code{printer-name} is used for non-PostScript printing. (There are two distinct sets of variables in case you have two printers attached to two different ports, and only one of them is a PostScript printer.) The default value of the variable @code{ps-lpr-command} is @code{""}, which causes PostScript output to be sent to the printer port specified by @code{ps-printer-name}, but @code{ps-lpr-command} can also be set to the name of a program which will accept PostScript files. Thus, if you have a non-PostScript printer, you can set this variable to the name of a PostScript interpreter program (such as Ghostscript). Any switches that need to be passed to the interpreter program are specified using @code{ps-lpr-switches}. (If the value of @code{ps-printer-name} is a string, it will be added to the list of switches as the value for the @code{-P} option. This is probably only useful if you are using @code{lpr}, so when using an interpreter typically you would set @code{ps-printer-name} to something other than a string so it is ignored.) For example, to use Ghostscript for printing on an Epson printer connected to the @samp{LPT2} port, put this in your @file{_emacs} file: @example (setq ps-printer-name t) ; Ghostscript doesn't understand -P (setq ps-lpr-command "c:/gs/gs386") (setq ps-lpr-switches '("-q" "-dNOPAUSE" "-sDEVICE=epson" "-r240x72" "-sOutputFile=LPT2" "-Ic:/gs")) @end example @noindent (This assumes that Ghostscript is installed in the @file{"c:/gs"} directory.) @vindex dos-printer @vindex dos-ps-printer For backwards compatibility, the value of @code{dos-printer} (@code{dos-ps-printer}), if it has a value, overrides the value of @code{printer-name} (@code{ps-printer-name}), on MS-DOS and MS-Windows only. @node MS-DOS and MULE @section International Support on MS-DOS @cindex international support @r{(MS-DOS)} Emacs on MS-DOS supports the same international character sets as it does on Unix and other platforms (@pxref{International}), including coding systems for converting between the different character sets. However, due to incompatibilities between MS-DOS/MS-Windows and Unix, there are several DOS-specific aspects of this support that users should be aware of. This section describes these aspects. @table @kbd @item M-x dos-codepage-setup Set up Emacs display and coding systems as appropriate for the current DOS codepage. @item M-x codepage-setup Create a coding system for a certain DOS codepage. @end table @cindex codepage, MS-DOS @cindex DOS codepages MS-DOS is designed to support one character set of 256 characters at any given time, but gives you a variety of character sets to choose from. The alternative character sets are known as @dfn{DOS codepages}. Each codepage includes all 128 ASCII characters, but the other 128 characters (codes 128 through 255) vary from one codepage to another. Each DOS codepage is identified by a 3-digit number, such as 850, 862, etc. In contrast to X Windows, which lets you use several fonts at the same time, MS-DOS doesn't allow use of several codepages in a single session. Instead, MS-DOS loads a single codepage at system startup, and you must reboot MS-DOS to change it@footnote{Normally, one particular codepage is burnt into the display memory, while other codepages can be installed by modifying system configuration files, such as @file{CONFIG.SYS}, and rebooting.}. Much the same limitation applies when you run DOS executables on other systems such as MS-Windows. @cindex unibyte operation @r{(MS-DOS)} If you invoke Emacs on MS-DOS with the @samp{--unibyte} option (@pxref{Initial Options}), Emacs does not perform any conversion of non-ASCII characters. Instead, it reads and writes any non-ASCII characters verbatim, and sends their 8-bit codes to the display verbatim. Thus, unibyte Emacs on MS-DOS supports the current codepage, whatever it may be, but cannot even represent any other characters. @vindex dos-codepage For multibyte operation on MS-DOS, Emacs needs to know which characters the chosen DOS codepage can display. So it queries the system shortly after startup to get the chosen codepage number, and stores the number in the variable @code{dos-codepage}. Some systems return the default value 437 for the current codepage, even though the actual codepage is different. (This typically happens when you use the codepage built into the display hardware.) You can specify a different codepage for Emacs to use by setting the variable @code{dos-codepage} in your init file. @cindex language environment, automatic selection on @r{MS-DOS} Multibyte Emacs supports only certain DOS codepages: those which can display Far-Eastern scripts, like the Japanese codepage 932, and those that encode a single ISO 8859 character set. The Far-Eastern codepages can directly display one of the MULE character sets for these countries, so Emacs simply sets up to use the appropriate terminal coding system that is supported by the codepage. The special features described in the rest of this section mostly pertain to codepages that encode ISO 8859 character sets. For the codepages which correspond to one of the ISO character sets, Emacs knows the character set name based on the codepage number. Emacs automatically creates a coding system to support reading and writing files that use the current codepage, and uses this coding system by default. The name of this coding system is @code{cp@var{nnn}}, where @var{nnn} is the codepage number.@footnote{The standard Emacs coding systems for ISO 8859 are not quite right for the purpose, because typically the DOS codepage does not match the standard ISO character codes. For example, the letter @samp{@,{c}} (@samp{c} with cedilla) has code 231 in the standard Latin-1 character set, but the corresponding DOS codepage 850 uses code 135 for this glyph.} @cindex mode line @r{(MS-DOS)} All the @code{cp@var{nnn}} coding systems use the letter @samp{D} (for ``DOS'') as their mode-line mnemonic. Since both the terminal coding system and the default coding system for file I/O are set to the proper @code{cp@var{nnn}} coding system at startup, it is normal for the mode line on MS-DOS to begin with @samp{-DD\-}. @xref{Mode Line}. Far-Eastern DOS terminals do not use the @code{cp@var{nnn}} coding systems, and thus their initial mode line looks like on Unix. Since the codepage number also indicates which script you are using, Emacs automatically runs @code{set-language-environment} to select the language environment for that script (@pxref{Language Environments}). If a buffer contains a character belonging to some other ISO 8859 character set, not the one that the chosen DOS codepage supports, Emacs displays it using a sequence of ASCII characters. For example, if the current codepage doesn't have a glyph for the letter @samp{@`o} (small @samp{o} with a grave accent), it is displayed as @samp{@{`o@}}, where the braces serve as a visual indication that this is a single character. (This may look awkward for some non-Latin characters, such as those from Greek or Hebrew alphabets, but it is still readable by a person who knows the language.) Even though the character may occupy several columns on the screen, it is really still just a single character, and all Emacs commands treat it as one. @vindex dos-unsupported-character-glyph Not all characters in DOS codepages correspond to ISO 8859 characters---some are used for other purposes, such as box-drawing characters and other graphics. Emacs cannot represent these characters internally, so when you read a file that uses these characters, they are converted into a particular character code, specified by the variable @code{dos-unsupported-character-glyph}. Emacs supports many other characters sets aside from ISO 8859, but it cannot display them on MS-DOS. So if one of these multibyte characters appears in a buffer, Emacs on MS-DOS displays them as specified by the @code{dos-unsupported-character-glyph} variable; by default, this glyph is an empty triangle. Use the @kbd{C-u C-x =} command to display the actual code and character set of such characters. @xref{Position Info}. @findex codepage-setup By default, Emacs defines a coding system to support the current codepage. To define a coding system for some other codepage (e.g., to visit a file written on a DOS machine in another country), use the @kbd{M-x codepage-setup} command. It prompts for the 3-digit code of the codepage, with completion, then creates the coding system for the specified codepage. You can then use the new coding system to read and write files, but you must specify it explicitly for the file command when you want to use it (@pxref{Specify Coding}). These coding systems are also useful for visiting a file encoded using a DOS codepage, using Emacs running on some other operating system. @node MS-DOS Processes @section Subprocesses on MS-DOS @cindex compilation under MS-DOS @cindex inferior processes under MS-DOS @findex compile @r{(MS-DOS)} @findex grep @r{(MS-DOS)} Because MS-DOS is a single-process ``operating system,'' asynchronous subprocesses are not available. In particular, Shell mode and its variants do not work. Most Emacs features that use asynchronous subprocesses also don't work on MS-DOS, including spelling correction and GUD. When in doubt, try and see; commands that don't work print an error message saying that asynchronous processes aren't supported. Compilation under Emacs with @kbd{M-x compile}, searching files with @kbd{M-x grep} and displaying differences between files with @kbd{M-x diff} do work, by running the inferior processes synchronously. This means you cannot do any more editing until the inferior process finishes. By contrast, Emacs compiled as native Windows application @strong{does} support asynchronous subprocesses. @xref{Windows Processes}. @cindex printing under MS-DOS Printing commands, such as @code{lpr-buffer} (@pxref{Hardcopy}) and @code{ps-print-buffer} (@pxref{Postscript}), work in MS-DOS by sending the output to one of the printer ports. @xref{MS-DOS Printing}. When you run a subprocess synchronously on MS-DOS, make sure the program terminates and does not try to read keyboard input. If the program does not terminate on its own, you will be unable to terminate it, because MS-DOS provides no general way to terminate a process. Pressing @kbd{C-c} or @kbd{C-@key{BREAK}} might sometimes help in these cases. Accessing files on other machines is not supported on MS-DOS. Other network-oriented commands such as sending mail, Web browsing, remote login, etc., don't work either, unless network access is built into MS-DOS with some network redirector. @cindex directory listing on MS-DOS @vindex dired-listing-switches @r{(MS-DOS)} Dired on MS-DOS uses the @code{ls-lisp} package where other platforms use the system @code{ls} command. Therefore, Dired on MS-DOS supports only some of the possible options you can mention in the @code{dired-listing-switches} variable. The options that work are @samp{-A}, @samp{-a}, @samp{-c}, @samp{-i}, @samp{-r}, @samp{-S}, @samp{-s}, @samp{-t}, and @samp{-u}. @node Windows Processes @section Subprocesses on Windows 95 and NT Emacs compiled as a native Windows application (as opposed to the DOS version) includes full support for asynchronous subprocesses. In the Windows version, synchronous and asynchronous subprocesses work fine on both Windows 95 and Windows NT as long as you run only 32-bit Windows applications. However, when you run a DOS application in a subprocess, you may encounter problems or be unable to run the application at all; and if you run two DOS applications at the same time in two subprocesses, you may have to reboot your system. Since the standard command interpreter (and most command line utilities) on Windows 95 are DOS applications, these problems are significant when using that system. But there's nothing we can do about them; only Microsoft can fix them. If you run just one DOS application subprocess, the subprocess should work as expected as long as it is ``well-behaved'' and does not perform direct screen access or other unusual actions. If you have a CPU monitor application, your machine will appear to be 100% busy even when the DOS application is idle, but this is only an artifact of the way CPU monitors measure processor load. You must terminate the DOS application before you start any other DOS application in a different subprocess. Emacs is unable to interrupt or terminate a DOS subprocess. The only way you can terminate such a subprocess is by giving it a command that tells its program to exit. If you attempt to run two DOS applications at the same time in separate subprocesses, the second one that is started will be suspended until the first one finishes, even if either or both of them are asynchronous. If you can go to the first subprocess, and tell it to exit, the second subprocess should continue normally. However, if the second subprocess is synchronous, Emacs itself will be hung until the first subprocess finishes. If it will not finish without user input, then you have no choice but to reboot if you are running on Windows 95. If you are running on Windows NT, you can use a process viewer application to kill the appropriate instance of ntvdm instead (this will terminate both DOS subprocesses). If you have to reboot Windows 95 in this situation, do not use the @code{Shutdown} command on the @code{Start} menu; that usually hangs the system. Instead, type @kbd{CTL-ALT-@key{DEL}} and then choose @code{Shutdown}. That usually works, although it may take a few minutes to do its job. @node Windows System Menu @section Using the System Menu on Windows Emacs compiled as a native Windows application normally turns off the Windows feature that tapping the @key{ALT} key invokes the Windows menu. The reason is that the @key{ALT} also serves as @key{META} in Emacs. When using Emacs, users often press the @key{META} key temporarily and then change their minds; if this has the effect of bringing up the Windows menu, it alters the meaning of subsequent commands. Many users find this frustrating. @vindex w32-pass-alt-to-system You can reenable Windows's default handling of tapping the @key{ALT} key by setting @code{w32-pass-alt-to-system} to a non-@code{nil} value.