Computer Displays

Screen specifications are given both in pixel width times height and diagonal screen size. Buying a larger display for your computer but keeping the same graphical adapter gives you a larger image. Because the bit maps stay the same, the "dots" just get bigger, and this means the resolution or clarity of the image decreases. It is the same as with a large TV screen. A smaller, 19-inch screen is quite suitable for a single user at a close distance, while a large, 34-inch display works well for demonstrations or classroom use where the viewers are far away (and therefore need a large image but cannot resolve the larger dots).

Some common display types, resolutions, and sizes are:

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DISPLAY CHARACTERISTICS

Macintosh SE

512 X 342, monochrome, 9'' diagonal

Macintosh II

640 X 480, 256 colors, 13'' diagonal

IBM PC, VGA

640 X 480, 16 colors, 12'' diagonal

IBM PC, SVGA

1024 X 768, 256 colors, 14'' diagonal

Sun SPARCstation

1150 X 900, monochrome, 19'' diagonal

IBM RS 6000

1280 X 1024, 256 colors, 19'' diagonal

HP Model 900

1280 X 1024, 256 colors, 16'', 19'' diagonal

A number of other factors also influence how readable the screen is. These include the refresh rate and the presence of interlacing. Typically computer displays are refreshed, or redrawn, at 60 to 70 Hz. A higher refresh rate means a smoother display for fast graphics. A common problem occurs when the room lighting and computer screen each flicker (strobe) near the same frequency, in which case the screen's flicker becomes noticeable. This is a common problem in the United States where there is 60 Hz fluorescent lighting in most offices.

    Interlacing is when the screen is drawn twice, the electron beam of the second drawing scanning between the lines of the first drawing. This is used to give television pictures and cheap computer displays increased resolution.