cdrom

cd-rom is the most safe storage devices.in market we can have it as CD or DVD-ROM. it is only readable that means once on CD data are written, it cannot be erease so for long term storage it can best  to used it.it has alot of advantages as it cannot be erase the data easily once it is filled. So in market we can haveCD of 700MB and DVD-ROM from4.7GB to 16GB.