System Configuration : System Setup : System Usage : Activity Meters

Activity Meters
All versions of Pro Tools provide three common system Activity meters. Avid HDX, Pro Tools|HD, and HD Native systems alsoprovide a meter for monitoring PCI activity.
 
System Usage window (Pro Tools|HD system shown)
PCI (Avid HDX, Pro Tools|HD, and HD Native Systems Only)
Displays the amount of PCI bus activity.
CPU (Native)
Displays the amount of CPU processing activity for host-based plug-in processing.
CPU (Clip)
Displays the amount of processing activity for Real-Time Elastic Audio processing and clip gain.
Disk
Displays the amount of hard disk processing activity.
As these meters approach their limits, host processing and recording or playback of automation data can be affected. If CPU or PCI Activity are high, a system error may occur. If Disk Activity is high, Pro Tools may miss playback of some automation data during particularly dense periods of activity, such as while using the Bounce to Disk command.