He might be thinking about ripping off DVD movies into his computer hard drives. If it is, then there's a better way to do that by using DVDSrhink

My question is why some one would do that in the first place. All computers today comes with a DVD drive.

now days it would most likely be HDMI input card.
some older computers have RCA jacks that would be left right stereo, and digital cable (red white yellow) (this would be stereo only).
Sometimes called a media player card.
It all depends on what type of audio video card is in the computer.
this type of card is not a common feature on computers because most would just have the DVD player built in.