IM adding a HDD or a SDD.

[kaito.takeda125]

Do I need to reinstall windows If i add a HDD or SDD?

 

[Gam3r01]

If you want to boot from those drives, yes.
If they are just for additional storage, then no.

 

[geofelt]

No, not for use as a data drive.
If you want windows on the new drive, the answer may be different.