Samsung LS21DPWAB-XAA - Manual (Page 31)

Menu Description
SOURCE
Selects the input signal while the OSD is off.
(When the source button is pressed to change the input mode, a message
appears in the upper left of the screen displaying the current mode --
Analog, Digital, AV, S-Video and Component input signal.)
Note : Changing the source is allowed only in external devices that are
connected to the monitor at the time.
PIP ( Available in Analog/Digital(PC) Mode Only )
Menu Description
PIP
Push the PIP button to turn PIP screen On/Off.
You can view a picture from AV, S-Video, or Component through the PIP
screen in Analog and Digital (PC) mode.