ps2 file size

[taffio]

does anyone know if it's my dvd rom or something else but when i make an image of getaway (ps2 dvd game) it shows up different file sizes on both my cd drives.

my 1 drive is a dvd-rom/cd writer whitch shows the game at about 4.4 gb and my pioneer 105 shows it has 4.2 gb,
it did'nt want to make an image on my combi but was ok on the pioneer.
it copied/played ok from the pioneer but dont know why shows different sizes.
thx

ps2 ver 4
magic 3
pioneer 105