The Disk Activity panel shows information on disk usage:
Activity Guages
Activity Gauge (1)
The percentage activity of the disk or partition with the highest read/write rates.
Activity Gauge (2)
The percentage activity of the disk or partition with the second-highest read/write rates.
Least Space
/name
The name of the mount point of the disk that has the least amount of free space, and that is not already 100% full. (Because of this, no CD-ROM devices are shown.)
Tip: You can configure this control to display the total and used space on ANY available disk on the system. Right-click the control and select Disk Options.
Total
The total amount of free space that has been allocated to this disk.
Used (MB/GB)
The amount of disk space that is currently being used by this disk.
Used (%)
The amount of disk space that is currently being used by this disk, expressed as a percentage.
Data flows between the Memory panel and the Disk Activity panel
Disk I/O (Memory to Disk Activity)
The number of writes that the system makes to disk per second.
Disk I/O (Disk Activity to Memory)
The number of reads that the system makes from disk per second.