Performance Monitor limits its' reporting percentage to 100%.

Some performance counters, like Physical Disk / TOTAL can exceed 100% when multiple drives exist.

Starting with SP3, the CapPercentsAt100 registry value allows reporting of percentages above 100%. Navigate to:

HKEY_CURRENT_USER\Software\Microsoft\PerfMon

Add Value name CapPercentsAt100, a type REG_DWORD value, and set the data value to 0. The default is 1, which limits the results to 100%.

NOTE: If the PerMon key does not exist, run Perfmon to create it.