Aspect ration being the most obvious difference on my setup, however something I was not expecting was a difference in sound.
In QemuLator a simple BEEP 20,5 produces a click
In QPC2 the same command produces a beep
This seems strange why there would be any differences, however on reading the manual it states
Since version 3.02, the beeper is no longer emulated through the PC speaker (this was only possible under Win9x/ME anyway) but through the soundcard by using the DirectSound interface. This way all Windows systems can benefit from the emulation. The emulation has been completely rewritten for this purpose and the sound is now quite similar to the original beep.
Sound emulation can be configured to be enabled (default), disabled, or enabled automatically. The reason this item is optional is that under some Windows versions DirectSound applications can work simultaneously with other DirectSound programs but not with old waveform applications. This means that after starting QPC, some applications can’t emit any more sounds, even when QPC is not beeping. Now the emulation can be completely switched off or, if you still want the occasional beep and have other applications work correctly, you can set it to “automatic” mode. In this mode, DirectSound is enabled before every beep and released again immediately. The drawback is that this procedure needs some time (there’s some “latency”) thus short beeps may simply get lost (i.e. the sound is switched off again before the soundcard has time react).
Furthermore, there is an option to set the default volume of the beeper emulation. This is useful because an emulated beep can be much louder than normal sounds.
So I guess using the soundcard makes the difference, where QemuLator pipes it through the PC speaker routine even though it ends up at the same point.
It would be interesting to know if the original BBQL and SMSQmulator produce a click or beep.