What Contributes The Most To System Boot Time?
I've always thought of instant-on operating systems and it seems that we're still far away from having those on our computers and mobile phones. Windows 8 I heard, has a boot time of about 8 seconds; which is quite amazing; but it's still far from being 'Instant'. Even the modern mobile operating systems like iOS & Android can't be called instant on operating systems.
Pardon my limited knowledge of operating systems and computer hardware; I want to know what contributes the most to system boot time. I'm also interested in knowing whether we have practical / impractical ideas to reduce to so as to take a step towards instant on Operating Systems. Looking forward to well informed responses.