It's double the size of a 500GB, but far as being faster, it depends on the RPM's, etc. If they are in the same family (as in both being WD Black's), there isn't a noticeable difference.
What does 1TB Mean as a size in Computing, AND How much bigger/faster than 500GB is 1TB?
1TB means 1 Terabyte. 1TB is equal to 1000GB in terms of storage. 500GB is half of 1TB
Because it stores more, doesn't mean it is faster. You want to look out for the RPM which means revolutions per minute. The faster the disc spins, the faster the hard drive operates, 7200 RPM is fast.
The faster portion depends on the type of hard drive the two are.
For example, your 500GB drive could be 4200 RPM and the 1TB could be 7200 RPM. The higher the RPM, the quicker it is. RPM stands for Revolutions Per Minute. The RPM numbers are examples, so you'll have to refer to your manufacturer's guide on how much the RPMs are for each of your drives.
The faster portion depends on the type of hard drive the two are.
For example, your 500GB drive could be 4200 RPM and the 1TB could be 7200 RPM. The higher the RPM, the quicker it is. RPM stands for Revolutions Per Minute. The RPM numbers are examples, so you'll have to refer to your manufacturer's guide on how much the RPMs are for each of your drives.
Both drives would be 7200rpm or 5900 or 5400 or 10000 since those are the standards! Size of a drive has nothing to do with what rpm it rotates at!
In raw capacity a 1TB drive is literally double the capacity of a 500GB drive.
A speed comparison is a little harder to quantify because it depends or the two specific hard drives you are comparing, in some cases there is no difference and in other it's huge. There are a lot of factors here ranging from who manufactured it to when it was manufactured but the main one is how it was manufactured. Today you have 1TB drive with a single platter which are no better than the 500GB from the same line. But todays 500GB has more than double the throughput of the original Hitachi 1TB hard drives when they were launched 5-6 years ago.
Lastly, what 1TB means depends on what you plan to use the computer for.
General office and web surfing - overkill, even a 250GB/500GB drive is overkill in most cases.
Music - still overkill unless your collection is massive.
Picture editing - should be plenty
Gaming - now we're talking, all those steam downloads will need somewhere to go, you may even need bigger drive after some time
Video editing/movies/programs - should be plenty when you start out but you will probably need extra storage after a while.