Commodore 128 System Manual page 16

Chapters II, III and IV, which include Sections 3 through 15, tell
you how to access and use the capabilities of the three powerful
and versatile operating modes of the Commodore 128 Personal
Computer.
Switching Between Modes
The following chart tells you how to switch to one mode from
another.
NOTE: If you are using a Commodore 1901 dual monitor,
remember to move the video switch on the monitor from
COMPOSITE or SEPARATED to RGBI when switching from 40
column to 80 column display. Reverse this step when switching
from 80 to 40 columns.
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