Many routers run a Linux OS and abrupt power failure can happen. Considering this - how do they handle the possibility of file system corruption caused by a power failure? If they make the system read only, how are you able to change settings?
Routers and other small linux devices do not use hard drives.
They use different types of RAM:
- DDR RAM as working storage
- ROM for system image (Kernel + OS)
- Non Volatile RAM for Settings (/dev/nvram)
In case of an crash they boot again and reinitialize the OS, so nothing get's lost.