Although most operating systems for PCs and servers support some modified
version of swapping, mobile systems typically do not support swapping in any
form. Mobile devices generally use flash memory rather than more spacious
hard disks as their persistent storage. The resulting space constraint is one
reason why mobile operating-system designers avoid swapping. Other reasons
include the limited number of writes that flash memory can tolerate before it
becomes unreliable and the poor throughput between main memory and flash
memory in these devices.