What's the difference between a solid state drive and an ordinary one?

I'm so fed up with PCs so I'm switching to a Mac but in building my laptop it's giving me the choice of a
750GB Serial ATA Drive @ 5400 rpm and a 128GB Solid State Drive so what's the difference between the 2 types and which one is better and why?
Update: Would this make a good laptop

2.8GHz Dual-core Intel Core i7
8GB 1333MHz DDR3 SDRAM — 2x4GB
128GB Solid State Drive
SuperDrive 8x (DVD±R DL/DVD±RW/CD-RW)
Backlit Keyboard (English) &
3 answers 3