This, is the shortest and simplest explanation.
- SSD (solid state disk). An HDD with no mechanical part (mainly composed of memory chips). Start getting its part as people Windows system (Priced pretty expensive if compared to its capacity)
- SATA III. The latest release of mechanical HDD which has the most fastest read and write among other mechanical drives. (speed and cache)
- SATA II. The recent HDD used widely, no need for explanation as everyone now is using it.
- PATA. An almost-come-to-extinction HDD that was around for many years (I still have it though).
The rest of its individual spec, just google it at its respective manufactures. (WD, Samsung, Seagate, Hitachi, etc)