I know it's sometimes overwhelming to try to figure out all the e-waste stuff, but Mechanic is right, you will do yourself a lot of good if you check out the old threads here. There are breakdowns on exactly what is in a hard drive so you can do your figuring by the separate metals that you're used to dealing with. Check out the old e-waste threads and use the search and you'll find a lot of info you can use. It's a lot of reading, but can save you from making a bad buy or missing a golden opportunity.