Display on 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 font-lock, Enriched Text mode, and others) by defining the relevant faces to use different colors. Use the list-colors-display command (see Frame Parameters) and the list-faces-display command (see Faces) to see what colors and faces are available and what they look like.
See MS-DOS and MULE, later in this chapter, for information on how Emacs displays glyphs and characters that aren't supported by the native font built into the DOS display.
When Emacs starts, it changes the cursor shape to a solid box. This is for compatibility with other systems, where the box cursor is the default in Emacs. This default shape can be changed to a bar by specifying the cursor-type parameter in the variable default-frame-alist (see Creating Frames). The MS-DOS terminal doesn't support a vertical-bar cursor, so the bar cursor is horizontal, and the width parameter, if specified by the frame parameters, actually determines its height. As an extension, the bar cursor specification can include the starting scan line of the cursor as well as its width, like this:
'(cursor-type bar width . start)
In addition, if the width parameter is negative, the cursor bar begins at the top of the character cell.
The MS-DOS terminal can only display a single frame at a time. The Emacs frame facilities work on MS-DOS much as they do on text-only terminals (see Frames). When you run Emacs from a DOS window on MS-Windows, you can make the visible frame smaller than the full screen, but Emacs still cannot display more than a single frame at a time.
The mode4350 command switches the display to 43 or 50 lines, depending on your hardware; the 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 n rows by m columns dimensions, it checks if there is a variable called screen-dimensions-nxm, 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 Set Video Mode function with the value of screen-dimensions-nxm in the 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 _emacs file:
(setq screen-dimensions-66x80 85)
Since Emacs
