The drive is called a hybrid hard drive, because it includes flash memory storage space in addition to the usual magnetic disk storage. The flash memory acts as a storage buffer, holding data until it's full and only then writing the data to the disk.
This cuts down on the amount of disk activity--typically the new drive spins only a few seconds every 10 or 20 minutes--which means battery life is extended by between 8 percent and 10 percent, according to Samsung's measurements.