Drive Scan versus Full System Scan

Hello,

I prefer to run a thorough Full System Scan at least once a week. However, a Full System Scan also scans my network backup drives resulting in a very long run...

Is a Drive Scan (for just drive C and drive D) as thorough as a Full System Scan? Or is a Drive Scan as light as a Quick Scan on the contrary?

Thanks in advance

SJW