"However, we need to make one thing unmistakably clear: the hard drive is still the main performance bottleneck in many application scenarios, and on all existing PC types. Whether you start Windows, launch applications or flip through large digital photos, you will always experience a delay due to the hard drive. The slower your hard drive is, the more noticeable the delay will be. Neither the fastest processor nor ridiculous amounts of RAM can change this fundamental equation.
Two issues turn this bottleneck into a real pain with small drives. First, the small platter diameter of 1.8" hard drives makes for low absolute rotation speeds. Second, the spindle speed of 4,200 RPM is already comparably slow: desktop hard drives spin at 7,200 RPM or more, and even 2.5" notebook drives are moving in this direction. Still, with energy requirements being a top priority in 1.8" product development, future products will probably not spin at faster speeds any time soon.
The bottom line is that there is an essential tradeoff between performance and physical characteristics. If you want an ultraportable PC using a 1.8" drive, you will forfeit performance."