Whats the Difference between FS and Main?

[Sam-TheMaster]

Fs is package or phones extra feature and prodcut special.
its like contant file or datapackage which includes extra facility..
like images sounds..themes views

where main arm or firmware is main OS which affects phone speed.
working accuracy. processs management.bugfixing.and manythig more as
out pcs software..

I hope i cleared...