What's the difference between a Dual Hard Drive and a Hard Drive?

Think of it this way, you could have one hand or two hands.

Thats what we're talking about one physical drive or two physical drives in the system.

Presently your system has one hard drive. I would just recommend you replace it alone here. But, if you needed more storage than one drive you could take your optical drive out and put a hard drive there. But! There is a down side here as you loose the internal optical drive to make room for the second drive.

Here is the IFIXIT guide you'll need to follow to replace your current drive: MacBook Pro 13" Unibody Mid 2012 Hard Drive Replacement.

Now what are you going to put in you have three choices

• Hard drive (HD)
• Hybrid drive (SSHD)
• Solid State drive (SSD)

Today most people put in a SSHD like this one: Seagate Laptop SSHD - ST1000LX001 as they gain the speed of the onboard SSD cache (32 GB here) but still have the storage space a standard HD offers (here 1 TB). This is the most economical. Cheaper is going with the traditional HD but you don't gain any real performance (like for like).

The other option is more costly but does offer more performance thats going with a SSD. Here a 512 GB unit will be more expensive than the 1 TB SSHD. I would recommend going with: Samsung 750 EVO 500 GB SSD as the best compromise between performance and cost. The other thing here is you do need to leave more of the drive free so the drive doesn't overwear one part. I recommend you leave at least 1/4 of the drive free.