Not sure the difference between RPM, RAM and graphics card

Hey everyone, newbie here.

I'm looking to buy a new desktop computer and I'd like to know whether the differences between the following two systems are worth a $200 difference?? Also, does the difference between Windows 8 / 8.1 matter?

My reason for buying the desktop is to watch a do school stuff (MS word and internet sites/stuff) and an occasional game (not too much of a gamer though, I think the most graphics-intensive game I play is DayZ LOL). No high-intensity graphics design, video editing or crazy-level gaming, just a casual gamer.

Is the difference between the two worth it?

1) $650
-Intel Core i5 4440
-8GB RAM
-1TB HDD, 7200 RPM
-Windows 8.1
<div>-

2GB AMD HD8570</div>
2) $450
<div>-

Intel Core i5 4440
</div>-6GB RAM
-1TB HDD, 5400 RPM
-Windows 8
<div>-

Integrated Intel HD</div>

Again, no high-intensity games, just school websites/documents/applications and a couple casual games, even a couple movies maybe (movies don't need to be HD).




Thanks for reading to this point I'd much appreciate the newb advice