Classic Computer Magazine Archive COMPUTE! ISSUE 132 / AUGUST 1991 / PAGE 53

Mouse resolution. (mouse devices)
by Richard C. Leinecker

Your computer's screen is composed of thousands of points called pixels. The number of pixels horizontally and vertically is often referred to as the screen resolution.

Mouse manufacturers typically list the resolution that their products are capable of in dots per inch (dpi). They might specify a capability of up to 1150 dpi or a capability of 10-1150 dpi. These numbers translate to the number of dots that the mouse cursor moves for every inch that you move the mouse. If you move the mouse one inch in a resolution of 300 dpi, the mouse cursor will move 300 dots.

How do dots relate to pixels? That depends on your monitor. To start with, check your monitor manual for its dot pitch specification. A typical dot pitch might be .29 points per pixel. That means there are about three dots for every screen pixel. If your mouse is set to 300 dpi, then moving the mouse one inch on your desk would move the mouse 100 screen pixels.

Your monitor's dot pitch isn't all you need to know; some video modes have pixels that are larger than others. In text mode, for instance, each text cell is really composed of eight pixels horizontally and vertically. That means that each time the mouse cursor moves in any direction, the mouse driver has registered the equivalent dot movement for eight pixels. Low-resolution CGA, EGA, and MCGA also have screen pixels that are larger. For these modes the mouse driver registers more dot movement for each pixel movement of the mouse cursor than for each pixel movement in higher-resolution modes.

Why buy a mouse with high-resolution capabilities? Some kinds of applications, such as computer-aided design (CAD) packages, require a very high degree of detail and input control. Using a mouse at lower resolutions would be like drawing with a crayon; the lines you draw wouldn't be any wider, but the lower resolutions would not afford the degree of control you'd need for sophisticated drawing applications. On the other hand, using a mouse at high resolutions would be like drawing with a precision writing instrument. The greater the resolution, the better your controls as you move around the screen.