DeviantPC has posted a review on the Asus CRW4012A (40*12*48) CD ReWriter

A point worth noting here is that most modern fast cd-writers use what's known as Zone CLV when writing. As the title of this technology suggests, the media is split into zones at which the drive records at different speeds. In the case of the CRW-4021A the disc is split up into 4 zones. The drive starts writing at 20x from the lead-in until the 8 minute point, then moves up to 24x until 26 minutes, then up to 32x until 52 minutes, and lastly to 40x at 52mins and stays there until the end of the burning process.

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