The System Usage window in Pro Tools is a great way to keep track of how hard your computer is working to keep your session running smoothly. It's a simple layout, but what is it really telling you?
CPU:
Ok, a bit self-explanatory. This is showing you the amount of processing power each core is using. Note, on M1 Macs this isn't properly reported, showing 4 cores. Im sure this will be fixed once Pro Tools is 100% certified on the M1s. Thanks to hyperthreading, this doesn't show the full picture, and Pro Tools is actually balancing the cores better than it admits here. You can use more advanced tools, like Activity monitor to show what's really going on under the hood, but for most users, verifying Pro Tools isn't struggling to get up the hill is enough. On the flip side, this can show you that something isn't quite right in the session- like buffer sizes, missing audio, plugin processing hogs, etc...
Activity:
This section is showing the amount of disk and memory usage. The aptly named "Disk" meter is showing the amount of disk processing being used. Disk Cache will show you the activity of the disk cache, only visible is using a fixed amount. Memory is indicating the total amount of installed ram Pro Tools is using.
If Memory is approaching 100%, you can reduce the usage by decreasing the disk cache, which will offload some of the audio to disk streaming, or install more ram...
Resources:
This section shows the number of voices being used by the session. There's a lot, and if you're running out, you can make unneeded track inputs and outputs inactive, make unused tracks inactive, thin some automation, or deactivate DSP plugins that aren't needed. In depth look at all of that to follow...
HDX card meters:
On HDX systems, this indicates how much of each chip is being used for DSP plugins and mixer loads.