How many threads for reading and writing to the hard disk?

Question

i am developing an application that gathers a list with all the files of the hard drive and also afterwards it does write files to the hard drive.

I want to ask : what i

Answer 1

Many of the answers refer to the amount of HDDs. Keep in mind that it also depends on the number of controllers. Sometimes two HDDs are managed by a single controller. Also: two partitions on the same HDD are not two HDDs!