From QB64.org wiki
The _AUTODISPLAY statement enables the automatic display of the screen image changes previously disabled by _DISPLAY.
- _AUTODISPLAY is on by default and displays the screen at around 30 frames per second (normal vertical retrace speed).
- _DISPLAY disables automatic graphic displays, but it also eliminates having to use PCOPY or page flipping when used correctly. Placing _DISPLAY after screen draws or other screen changes assures completion of the changes before they are displayed. The speed of QB64 code execution makes this a viable option.
- The _AUTODISPLAY (function) can be used to detect the current display behavior.