VirtualAcorn Technical support:
Stuttering keyboard or mouse
On a very few machines we have seen a problem where the keyboard or mouse can stutter. Typically the mouse will show the fault first. The problem manifests itself with a couple of symptoms. Firstly the mouse will suddenly stick and refuse to move for up to a couple of seconds. Secondly it will then free up and move normally for a period before sticking again.
There are two possible causes and two solutions to this problem. Try the Audio solution first, if this doesn't work try the Processor Priority solution.
The Audio problem
Ths stuttering could be caused by an Audio problem. RISC OS plays sound continuously, even if there is no sound that needs to be output, the sound system will still be running and playing silence. This can cause some audio devices, especially external USB sound cards, to have problems. This causes VirtualAcorn to stutter. What happens is that the sound card can't keep up, so audio isn't played. This can cause RISC OS to stop momentarily whilst it waits for the audio to complete properly.
To solve the problem you need to turn off the VirtualAcorn sound. Load VirtualAcorn and switch to a window with Alt and Enter. Go to the VirtualAcorn Tools menu and click on Options. Go to the Audio tab and untick the Enabled button. Now click Apply, then click OK. Now quit and re-load VirtualAcorn.
The Processor Priority problem
Windows has the concept of thread priorities. The higher the priority the more CPU time a task can grab, if it needs it. So what can happen is that a task with a higher priority can suddenly "steal" all CPU time from tasks with lower priorities. The result is that VirtualAcorn, with a low priority, can get stopped for a moment, hence the stuttering.
This Knowledge Base Article explains how to alter the processor priority.