Why so small sized dvds?

vbimport

#1

I just began writing dvd’s and i bought sentinel and tdk media,that have 4.7 gb written on them.

A friend said that they write only on 4.6+something…and i said,okay nho prob.
BUT NOW I SEE I CAN ONLY WRITE AT 4.483!?!
THEN WHY 4.7???
can i have a problematic drive/media?