CPU power consumption has also improved steadily during the last decade with new chip processes, shrinking feature sizes, and lowering voltage levels. Operating systems have also become more efficient. Transmeta's voltage and clock rates can be changed on the fly, and their benchmarks show substantial power saving over x86 processors at comparable application speeds. The REB claims 20-40 hours between charges, depending upon settings and usage, and the SB claims 5 hours. These are respectable figures using today's technology, and we can look forward to improvement.
Storage is another key element.
The speed, capacity and cost of flash storage used in these devices have improved steadily over time, and it has been used in many portable devices, including today's E-books. This is sufficient for reading on a plane or a weekend vacation, but it is not the lifetime library Vannevar Bush dreamt of. Price falls by around 50 percent and capacity doubles every year or so. Screen technology has not improved as quickly as electronics or storage. On the other hand, it is fine for more limited reading, and its small screen saves power, allows a slower processor than the SB, and results in a smaller, lighter device.