I have recently bought an external hard drive and with some difficulty eventually managed to back up my c drive. The d drive is almost full - do I need to back this up now? As my f drive is now my default back up drive, what purpose does the d drive now serve?

What is on the D: drive? And is it a partition on the internal drive?

Hi Occasional Visi, welcome to the board.

Backing up the C drive is backing up the operation system in case of a crash, then you can restore it as it was without going through lots of trouble. Similarly, if you have all you data such as important documents and photos in D drive you like to back them up in case something happens; you can just back up the files instead of backing up the whole drive. Hope this will help.