Sony has always been a big player in the optical storage market and it is mainly through the efforts of this company that MO (magneto optical) has lasted as long as it has. However, it is generally accepted that 14X MO signals the last phase of this format as physical limitations make it impractical to develop it further. Along with Plasmon, Sony has dived headfirst into development of blue laser optical products and as well as being one of the first to deliver a Blu-Ray Disc product to the Japanese consumer market has also launched its PDD (Professional Disk for Data) family of storage devices.

Sony casts its net over a wider market than Plasmon as along with document and email archiving it targets applications such as network and server backup for small to medium businesses. By designing its UDO drive to have the same physical form factor as MO, Plasmon is concentrating primarily on the enterprise market and those companies looking to migrate smoothly from MO.

Although a blue laser is at the heart of these three new formats it’s important to note that Blu-Ray, UDO and PDD are not compatible in any way. However, to add to the confusion PDD does use many of the same features as Blu-Ray. Built around the 405nm blue-violet laser, PDD also has the same 0.85NA (numerical aperture) as Blu-Ray. This allows it to use a smaller laser spot than UDO so disk capacity should be greater. However, whereas UDO uses double-sided disks for a total capacity of 30GB the Sony PDD disk is single-sided and offers a lower maximum of 23GB of storage space.

With the 0.85NA lens producing a shorter depth of field the protective substrate had to be reduced to only 0.1mm but Sony reckons the advantages of this are an improved tolerance to disks tilting or bending so increasing reliability. However, as with UDO the PDD disks cannot be subjected to the same treatment as CD or DVD media and Sony has taken the issue of contamination very seriously. The anti-static cartridges are very well constructed and protect the PDD media with a special revolving shutter mechanism. The external drive on review delivers the classy styling and quality manufacturing we now expect from Sony. The loading slot uses a dual shutter mechanism and even the mounting screw holes won’t let dust and dirt in.

The quoted performance for PDD is 11MB/sec and 9MB/sec for read and write operations respectively – double that of Blu-Ray and higher than the 8MB/sec read and 4MB/sec write speeds of UDO. Sony advised us it achieved these rates by using higher-quality media and improved drive electronics. The drive also uses a combination of CAV (constant angular velocity) and CLV (constant linear velocity) and can swap between modes to deliver the best performance. You can also hard-set the mode using a bank of DIP switches at the rear of the chassis.

Installation is simple enough and made a lot simpler by the fact that PDD disks only use a 2KB sector size. Consequently, you can install the drive on any Windows platform as it doesn’t need the hotfix required by UDO and on our Windows Server 2003 system the PDD unit was immediately identified as a removable drive. Sony recommends running a full format on each disk to prepare them but bring a good book with you as this process takes over 90 minutes. Even so, we found performance was superior to UDO with tests using the open-source Iometer returning 10.4MB/sec and 4.3MB/sec for sequential read and write operations. Securing and restoring our 690MB test video file also proved to be faster than UDO with these tasks delivering average transfer rates 4MB/sec and 10MB/sec respectively. We were unable to test True-WORM performance as, at the time of writing, Sony had yet to decide on the software bundle that will support this function.

As we observed in the Plasmon UDO review, the current blue laser optical products are all aimed at distinctly different markets. This does mean you don’t have a lot of choice at the moment but small to medium businesses looking for the next step in data archiving will find Sony’s solution the best bet.


It’s early days in the development of blue-laser optical storage devices but PDD clearly has the measure of UDO in the performance stakes. There’s not a lot of difference in price between the two but Sony’s alternative does look a more sensible choice for small to medium businesses and it doesn’t need any Windows patches either.