Check out the above picture. the HDD just is slightly taller than a AA battery. but its capacity can be up to 320GB. Here is the first 1.8-inch hard disk with 320GB capacity manufactured by Toshiba.
The HDD coded MK3233GSG features a 3Gbps SATA interface, 16MB buffer size and a rotary speed at 5,400RPM.
According to Toshiba, the mass production will start in December this year.