Why is an operating system software loaded from hard disk than from a rom chip?
I was asked this question and I am unable to find the answer.
Can someone explain?
The easiest answer is ease of patching and extensibility. ROM cannot easily be patched - though with some permanent storage location and some creativity and foresight when building your initial ROM, you can patch it with some hook code.
Size of ROM isn't a great answer. CD/DVDs are a permanent location and could be used, though not ROM 'chips'. ROM chips can be made large enough to handle an OS (heck some versions of Linux fit on floppies not too long ago) and wouldn't be that expensive, though worse than a DVD for distribution costs.
Replacing an OS via a new ROM chip isn't that attractive, but if you just plugged in a new PCI card, would that be so bad? We do that already so this isn't a great argument either.
Access speed to a ROM chip, generally, will be much superior than to a harddrive so you would get a performance boost this way, so that's actually a plus. Also having a ROM makes it that much harder for malware to infect the OS - another plus.
So, in general, I see many pluses for a ROM based OS vs a RAM based one. Nice question.