Not one drive does this on its own. All require the hardware then some software and most if not all the time some action on your part to make the backup happen.
For me I get by with a SYNC APP. There are so many that I can't choose for you from Roadkil's Unstoppable Copier, Syncback, and so many others that sync only the file changes from what folders you specify.
As to the actually HDD I will flatly pan any Seagate. Try the usual Toshiba Canvio.
https://www.amazon.com/s?k=toshiba+canvio+basics+2tb+portable run about 60 to 80 dollars.
So I have a windows 7 computer that I would like to back up. I have never been very good with updating and saving my data, but lately I feel it's important so I am looking to buy a good quality EXTERNAL hard drive.
My requirements. Needs to be 2TB at least, needs to be around the 60$ range (I don't mind bargain hunting).
The most important thing which I need to my hard drive to have is this. I would like a hard drive that can sync with my computer and know which new data is new and only save the new data. I don't want to have to delete and reload all the data from scratch every single time I want to "update" it. I'd imagine this type of thing is possible but I don't know where to look.
Really hoping someone tech savy can point me in the right direction. Thank you.