MacBook – What kind of SSD is compatible with the 2010 Unibody MacBook

It is a variant of Mini PCI Express & mSATA:

Some notebooks (notably the Asus Eee PC, the MacBook Air, and the Dell mini9 and mini10) use a variant of the PCI Express Mini Card as an SSD. This variant uses the reserved and several non-reserved pins to implement SATA and IDE interface passthrough, keeping only USB, ground lines, and sometimes the core PCIe 1x bus intact.[11] This makes the 'miniPCIe' flash and solid state drives sold for netbooks largely incompatible with true PCI Express Mini implementations.

Source: http://en.wikipedia.org/wiki/PCI_Express#Mini_PCI_Express_.26_mSATA

I have a late 2011 15" 2.2 quad core i7 macbook pro, and after using it with a 7200 rpm hard drive for about 2 months I decided to upgrade it to the Seagate Momentus XT 500GB Hybrid drive. I am a iOS programmer and I can't tell you what a big difference this hard drive made in my computer. I did a couple of tests before I changed out my old hard drive like boot up time and opening programs and such. With my 7200 RPM hard drive my boot up time was 31 sec. and with the hybrid drive my new boot up time is 20 sec. I strongly recommend the hybrid drives. Seagate also just updated there hybrid drives with twice the amount of solid state memory instead of 4 GB they now have 8 GB. I hope this helps!