Why can't we have DVD CAV writing at all speeds?



What are the mechanical or electronic restrictions to having a DVD burner that writes in full CAV mode regardless of the recording speed?


Hi rjih :slight_smile:

What do you mean by “full cav mode regardless of the recording speed” exactly? I dont quite get it, although it might be only me.


I think he means PCAV but am not sure either.


I think he means, “Why can’t we have drives that write @ 1,2,4,8 & 16x all at CAV?”, instead of ZCLV@8x, CAV@16x etc…

Well, its much more difficult to write @ higher speeds on the outside of the disc than it is at the inside, thats why one usually gets more errors on the outside…

CAV involves the disc spinning at a constant rotational speed, say, Constant RPM, which means, more area is read/written per given amount of time on the outside than on the inside… The inside tracks on a ~40x CDRW is written at ~18x whereas the outside is written at ~40x in CAV. It would actually be faster to write the whole disc at 40x in CLV (start at 40x, end at 40x)… but, the disc would probably be spinning so fast while writing/reading on the inside, that the least bit of imperfection could cause the disc to shatter. Therefore PCAV and ZCLV…

per the cdspeed2000 faq, CAV is not the fastest method of reading/writing… so it might not be beneficial to have CAV at ALL speeds…

Maybe someone can explain it better…


My best guess is the Z-CLV is a more tried-and-true method. CLV-type writing has been in use for much longer in DVD burning. Additionally, it’s easier to control for laser power calibation in CLV-type burning, because all you really need is one set of calibration for each of the speeds, wherease for CAV, your speed is continuously changing, and it is conceivable that continuing adjusting the laser power is more difficult than continuously adjusting the motor speed.