Question about visible fine circle on unburned DVDs

[jimdagys]

I am experimenting with different brands of blank DVDs. All are bought in China and have the code from Imgburn log as (Disc ID: TYG02) (Speeds: 4x, 6x, 8x, 12x) but are marked 8X, however, I think the Chinese just put that disk code on many kinds of blank DVDs, even if the burning area looks different (and therefore must be different types of disks). The brand that I am using now is called "banana", and has a picture of bananas on the disk. One thing I notice about these disks (unburned disk) that I didn't see on the last disks (with same code) is a very visible fine line circle about 0.5cm diameter larger than the initial inside burning diameter. See screenshot for simulated image of this circle.
After burning, the circle seems to disappear. My question is: what is the purpose of this circle?

[Baldrick]

Moving you to our Media section.

[MysticE]

code from Imgburn log as (Disc ID: TYG02) (Speeds: 4x, 6x, 8x, 12x) but are marked 8X, however,

ImgBurn is telling you what speeds your burner can burn these at. They are 8X discs.

[redwudz]

The inner most part of a DVD is for the power calibration area. The burner does a test burn to calibrate the laser power to the disc. I don't know if that's what you are seeing, but all DVDs have that area. There may also be some specific information written there by the manufacturer. The line you see may just be where the actual blank part of the disc begins.

[lordsmurf]

What redwudz said.