Martina wrote:

Hi!
Thank you for your help. Your suggestions have led me to do several things.
I run an Intel Pentium 4 with 3.0 GHz wich for some reason appears twice in my hardware manager (Win XP home). I have tried deinstalling one of them, but Windows insists on showing it twice. After several attempts and reboots

[...]

Yep, its always good to reboot Windows! :-(

Looks like you have the Intel "Hyperthreading" ("HT") enabled in your BIOS. That is where your one physical CPU acts as though there are two (logical) CPUs. You get a small overall performance boost by using HT.

Boinc was correct in assigning two WUs at the same time. You get one WU working on each of the two logical CPUs (the HT trick for the one physical CPU). Best is to set you CPU limit for boinc to be 2 again. Otherwise, you will see only '50%' utilisation of your system.

You should see two CPUs reported in your 'task manager' (use ctl-alt-del to get it).

Sorry, HT is indeed a confusing trick all round...

Happy crunchin',
Martin