It looks like the default value is 2, to give priority to foreground applications. That’s what I have on my work machine, an presumably my home machine as well though I’m not there to check.
PriorityControl Entries
The PriorityControl key defines the foreground/background priority boost differential. Change this value by choosing the Tasking button in the System dialog box in Control Panel. Values are stored under this Registry path:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\PriorityControlWin32PrioritySeparation REG_DWORD 0, 1, or 2
Default: 0x2Specifies the priority to give to the application running in the forground. This application receives more process or time relative to other applications running in the background. The values here correlate to the following options in the Tasking dialog box:
Value Meaning
0 Foreground and background applications equally responsive
1 Foreground application more reponsive than background
2 Best foreground application response time