In Windows, is 0 valid PID for a process or is it reserved by OS? It would be nice if you can provide a link to a doc that says it is reserved or what. Thank!
+2
A:
Open task manager - switch to the processes tab (maybe click "View", "Show columns" and enable the PID column).
PID 0 is the System Idle Process. Since that process isn't really a process and never exits, I suspect that it is always the case.
No documentation available to me, but I'm pretty certain this is always going to be the case.
developmentalinsanity
2010-07-12 21:41:41
A:
The PID of 0 is reserved for the Idle "psuedo-process", just like PID of 4 is reserved for the System (Windows Kernel).
I can't find any documentation on where that is specified, but querying the processes via any API (Perf Counters, WMI) will always give you the idle process for PID 0.
codekaizen
2010-07-12 21:48:28
A:
It's not stated anywhere but it comes down to how the kernel handle table works. This same object is used for both process handles and process/thread IDs. It happens that handle values all start at 0x4, and PsInitialSystemProcess is the first process to be created, so it gets a PID of 4. Idle process isn't actually a process and you can't open it. It probably doesn't have a PID for most intents and purposes but most tools consider it to be 0.
wj32
2010-07-12 21:58:33