Default [Q] are speed rebirth custom part 1 and part 2 different?

i have seen in the link of the speed rebirth custom rom.
there are three links available... 1 is for speed rom on official xperia c
2 is speed rebirth custom part 1 and
3 is speed rebirth custom part 2

i want to ask that are the custom part 1 and part 2 different roms or do we have to merge them before flashing the rom???