Kernel is basically the heart of an OS (Operating System) ..
It handles all the low - level stuff .. it is the middleman between your applications and the actual harware .. it interacts with the hardware and controls them..for eg the CPU, RAM me...
uhmm since the MIUI4 port is built upon Maclaw's CM9 port..
it has got no camera as of now..!
but the battery problem has been solved..maclaw's CM9 has a damn good battery life now! :)
It was a problem of CPU deep sleep..which he fixed it in ...