You need a Usb port.
They have different capacities from 128 Mb to 4 Gb.
They are very easy to carry and they are very faster.You can store all kind of files and folders.
You can also store programs, also you can install in another computer or in the pen drive itself.
They are becaming cheaper, and cheaoer day by day-Nowdays you can get a 2 gb pendrive fot less than 20€.
They are two different types of DVD:
DVD- ROM RD (read only memory) capacity from 2gb to 8 gb
DVD – ROM RW (rewriteable)_The capacity is 4,7, but you can only usea 4,3 GbThe are also double layer Cds and DVDs.