IBM ThinkPad 310E User Manual page 171

Basic System Settings
Note:
If the computer resolution is set at
640x480, the image on the computer
LCD and external monitor will not be
full-screen. For full-screen image,
set-up the computer LCD at 800x600
resolution.
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IBM ThinkPad 310E/310ED: User's Guide
Boot Display
If you connect an external monitor, you can switch display between
the LCD and the external display. This parameter determines which
display device the computer uses on boot-up. The following table
describes the settings.
Setting Description
Auto If an external display is present, the computer uses the
(default) external display; otherwise, the LCD is the display device.
Both The computer uses the external display and LCD
simultaneously.