System Configuration : System Setup : System Usage : Cache Meters

Cache Meters
(Pro Tools HD and Pro Tools with Complete Production Toolkit Only)
Pro Tools HD provides two meters in the System Usage window for monitoring the Disk Cache: Disk Cache and Timeline Cached. These meters are only present if a fixed Cache Size is selected in the Playback Engine dialog.
 
Disk Cache
Displays the percentage of how much of the allocated disk cache is filled. For example, if the Cache Size in the Playback Engine is set to 1 GB and a session uses 250 MB of audio files, the Disk Cache meter reads 25%. If all of the audio in the session is cached (including files in the Clip List that are not on the timeline), the Disk Cache meter appears green.
Timeline Cached
Displays the amount of audio in the session Timeline cached in RAM.
If the selected Cache Size in the Playback Engine is the same or greater than the amount of audio on the Timeline, the Timeline Cached meter reads 100% and it appears green (indicating that all of the audio on the Timeline is cached in RAM). This is useful for letting you know how much audio can still be added to the Timeline and be cached in RAM.
If the total amount of audio in the Timeline is more than the selected Cache Size in the Playback Engine, the Timeline Cached meter shows the percentage of audio on the Timeline that is cached in RAM. For example, if the selected Cache Size in the Playback Engine is 256 MB and the amount of audio on the Timeline is 1 GB, the Timeline Cached meter reads 25%.