Dual-Scan Displays

The dual-scan display (also known as a passive-matrix display) consists of transistors running down the x- and y-axis of the screen. The number of transistors determines the screen's resolution. The two transistors that intersect on the x- and y-axis control each pixel on the screen.

If a transistor fails, the entire line of pixels is disabled, leaving a black line across the screen. There is no way to repair this problem except to replace the display. The term dual-scan is derived from the fact that the processor redraws half of the screen at a time, which speeds up the refresh rate a little.

Dual-scan displays are considered inferior to active-matrix screens because they tend to be dimmer. For this reason, portable computers with this technology are becoming rare. They work by modifying the properties of reflected light rather than generating their own light. They are also more prone to ghost images, and it is difficult for two people to see the screen at the same time, because these displays can't be viewed well from an angle. The standard size for this type of screen is 10.5 inches (measured diagonally) with a resolution of 640 × 480. New systems are available with 12.1-inch and larger displays that have a resolution of 800 × 600.