Vertical-synchronization mechanisms

[twipley]

Sorry to kind of duplicate and repost underlying-mechanics wonderments here, but I believe putting this here may contribute to a certain visibility gain:

Running a Windows-XP guest under an Oneiric-Ubuntu host, I have noticed that emulator games played without ticking "enable vsync" in the emulator settings do not feature "tearing" as I would have expected.

Being the Linux newcomer that I am, and also quite a computer-software layman, I had two prominent questions in mind:

(1) what is it that applies vertical sync to the guest output? Is it the VirtualBox mechanisms, or the Ubuntu operating system?

(2) is the automatically applied vertical sync that I am experiencing, in terms of quality, equal or similar to the ones guest-machine software (for example, entertainment-system emulators) provide?

(3) is not vsync wrongly applied twice on top of one another in the case it is left activated in software-level options?

[mpack]

In that case I will lock the other thread, as cross posting is not allowed.

[twipley]

After some testing, I believe VirtualBox does nothing but grab the host-OS vsync setting and then feed that back to the applicable piece of guest software.

For example, if the answer is "yes, host vsync flag is set to 1," then update the display using complete frames only.