NIST expert: Don't max out DVD disks

When burning an optical disk, leave the last 10 percent of the disk empty to ensure greater compatibility with other disk drives, according to Olibh'ar Tadhg O'Slattra, a National Institute of Standards and Technology technical staff member who specializes in testing CDs and DVDs.

O'Slattra made the recommendation while presenting a study he and other DVD compatibility committee members of the Optical Storage Technology Association conducted on the current state of DVD equipment compatibility. O'Slattra spoke last week at a meeting of the Government Information Preservation Working Group.

Researchers found that compatibility among different DVD technologies has improved dramatically in the past six years, and users can take basic steps to assure even greater compatibility.

The project measured how well different brands of DVDs worked in different brands of DVD players. The researchers recorded data onto a variety of rewritable DVDs' in DVD-R, DVD-RW, DVD+R, and DVD+RW formats'using a variety of DVD burners. Then they tested each disk on every other DVD drive to see if the drive read the data correctly.

In this test, 91 percent of the combinations of disks and disk readers worked seamlessly. The result is a dramatic improvement over the results of a similar 1999 test, where the group found compatibility in less than 30 percent of the combinations.

Almost none of the failed tests were due to bad media or faulty drives, according to O'Slattra. Instead, the failures were due to incompatible 'burner/media combinations,' he said. In other words, the disks in the failed tests worked in other burners, and the burners worked without problem with other types of disks.

Of the failures to read a disk, the vast majority were due to a phenomenon O'Slattra called the 'edge effect,' or failures that happen at the edge of a disk. The group found that out of the 50 failures they recorded, 38 happened in the last 10 percent of the disk, and many of those within the last 5 percent of the disk.

'It was the very outer edge of the disk that was having significant problems,' O'Slattra said, noting that when edge effects are factored out, the compatibility rate jumps to 98 percent.

O'Slattra said his team has no conclusive theory for why all these errors happen at the end of the disk. He speculated that one factor may be that a spinning disk wobbles more at the edges, leading to the misreading the material.

To ensure a disks work with the widest range of drive readers, O'Slattra advised not filling disks to maximum capacity. 'If you [use] 90 percent or so of the disk, you should get very close to 100 percent compatibility,' O'Slattra said.

The quality of the disks themselves also had an impact on compatibility. O'Slattra noted there was a big difference between the failure rates among the different brands. The best disks worked in all the available players, whereas lower quality disks only worked 80.5 percent of the time. O'Slattra did not reveal the names of the individual brands.

While the results speak well for the interoperability of DVD products, O'Slattra said users could take extra measures to assure even greater compatability. In addition to only filling 90 percent of a disk, O'Slattra recommended that users update the disk reader's firmware. He also suggested that DVD device manufacturers should list the blank media that work best with their products.

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