wow. I learn so much from you guys...
well, if the limit of a power cable is 5 W, I guess that's the answer there.
That's the limit for external USB drives. But the point is, if an external USB one is limited to 5W an internal one of comparable vintage and speed probably isn't a *whole* lot worse. Early external burners required their own power brick, so they've definitely reduced the power requirements over the years.
as for the speed, are modern drives CAV or CLV? and doesn't the outside of the disc spin faster and read data faster as a result?
When operating in data mode they are CAV, and yes the outer area of the disc has higher throughput as a result. This is why the maximum throughput spec for DVD drives is rarely achieved in practice -- you only get the rated maximum speed when burning/reading the outermost area of a nearly full disc! Although the drive is nominally CAV, spindle speed can still be ramped up/down for power management purposes, due to user request (e.g. reduced burn speed to improve the reliability of the burn), or when the drive is attempting to recover data from a marginal sector.
When playing audio and video discs the drive switches to CLV mode, since it needs to maintain whatever bitrate the content was encoded at.
If the world isn't making sense to you, you're either drinking too much or not drinking enough.