What does the "PF" in the "PF usage" stand for?

when i open my windows task manager....i see 2 things showin' under the performance tag... one is the CPU usage with which i am ok....the other one is "PF usage".....for which i have no clue... plz help me out on what does it stand for? and how much of its occupancy is normal for my PC with a... show more when i open my windows task manager....i see 2 things showin' under the performance tag...

one is the CPU usage with which i am ok....the other one is "PF usage".....for which i have no clue...

plz help me out on what does it stand for? and how much of its occupancy is normal for my PC with a 512MB RAM......
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