Keep your PS3 disc for these $10 PS4 game upgrades

If you want to upgrade these four PS3 games to their PS4 counterparts, you'd better hold onto the discs. Sony revealed how those who buy Assassin's Creed 4: Black Flag, Battlefield 4, Call of Duty: Ghosts, or Watch Dogs will get a next generation discount on the PlayStation Blog this week.

If you buy your game of choice on disc, it will come with a PlayStation Store code. After you input the code, you'll be able to download the game on PS4 for $10, but keep in mind you'll need to keep the PS3 disc in the system to activate and play it.

It's an interesting cross-gen compromise which will cut down on secondhand sales, and it also reveals that PS4 is capable of reading PS3 discs. We'll see if Sony does any more with this functionality down the line--like letting you stream those games once the backwards-compatibility library opens in 2014, for instance.

Or if you buy the PS3 version digitally, just pay $10 on PS4 and you can download the new version straight away.

However you do it, keep in mind that this is a limited time promotion: you have until January 31, 2014 for Assassin's Creed IV and Watch Dogs, March 28 for Battlefield 4, and March 31 for Call of Duty: Ghosts to input the code and make the purchase.