Have a look at what came before Symbian : Psion series 5

In the end, when the Series 5 finally shipped, it was like being transported into the future, only through a very murky tunnel.

Gretton’s hardware clocked in at a meagre-sounding 18Mhz — but performed like a desktop Intel PC from just two years previously — and it could still maintain 30 hours use on two AA batteries. Once the circuitry was complete, the Series 5 performed the same tasks as its Windows CE rivals but used only a quarter of the power.

I still have two working Psion 5MX palmtops and love them to death.