I know what the disk io, disk queue length and other measures are, but what does 'Highest active time' mean?

Is it the amount of time it is busy handling requests, or something else?

When it is high, does it mean the CPU is busy doing some IO work, or is it just indicating that the disk is busy handling requests?

I'm trying to work out if 50% active time means that 50% of the time the disk is either seeking, reading or writing, rather than the kernel is spending 50% of it's time servicing IO requests.

Edit Another quick data point here. If you look at the difference between an SSD and a physical disk, the SSD has significantly less activity, so I guess this really means the amount of time the operating system is waiting for the disk to respond and returning data.