Graduated write speeds

[dbminter]

Why is it most drives write media like 8x DVD+RW and 8x DVD+R DL's at graduated write speeds?

 

 

I know it's based on the write strategies on the disc/in the drive, but some drives don't write at these gradually increasing speeds.  Sony/Optiarc wrote 8x DVD+RW and 8x, not starting at 6x and then eventually going to 8x.  They also wrote 8x DVD+R DL at 8x, not starting at 4x, then going to 6x, and then to 8x.

 

 

So, why the graduated write strategy?