Well a ROM is as the name suggests..READ ONLY MEMORY and a RAM is RANDOM ACCESS MEMORY so basically any thing written on the ROM will not allow u to make any alterations in its MEMORY (wat ever is written on the Disc) like u hv it in games CD wich r on a CD ROM and hence u cannot change/delete/modify those files wich r on a ROM..
Well the same concept is for DVD ROM and DVD RAM drives..bro....i mean the difference is between the ROM and RAM...formats...
cheers n e-peace....