New Western Digital format squeezes 11 percent more capacity from drives

WD Caviar Green

Western Digital (WD) is beginning to use a new hard disk drive format that opens up between 7 percent and 11 percent more capacity on hard disk drives, meaning a 1TB drive could gain more than 100GB in capacity.

The disk expansion technique, known as Advanced Format, takes advantage of industry changes in drive sector sizes to consolidate overhead information and free up that additional space for data storage. Advanced Format is also being adopted by other drive manufacturers to wring more capacity out of existing hard drive technology.

There are three basic methods for increasing capacity on a hard drive: increase the bit density; increase the number of tracks per inch; or increase the number of surfaces (i.e. disk platters). WD chose to boost bit density because it takes advantage of additional space already available on every track of a hard disk drive platter, the company said in a document posted on its Web site.

Hard disk tracks are currently composed of 512-byte sectors. But for efficiency reasons, the industry as a whole is moving to larger sectors that store 4,096 bytes of data. Each sector on a drive has a natural gap that contains Sync/DAM (lead-in) and error correction code information (ECC). Multiple blocks of ECC require a lot of overhead.

The Advanced Format removes Sync/DAM blocks that handle data addressing, inter-sector gaps and eight separate blocks of ECC, and consolidates that overhead into one block on the drive, gaining the extra disk space when compared to traditional formatting, the company said.

WD said Advanced Format also increases data integrity by providing a more efficient error correction scheme by using longer ECC code words, improving error correction by 50 percent, according to WD.

Currently, WD’s Caviar Green, which are available in capacities of up to 2TB, are being built using Advanced Format. WD said more models and capacities will be added in the future.

Advanced Format is designed to work with Windows Vista, Windows 7 and Mac OS X; it’s not optimized for Windows XP or older operating systems. For users on older OSes, the company’s WD Align software utility. After a user installs the operating system or partition on one of the new Advanced Format drives, the software takes about 20 minutes to create partitions that ensure the drive runs at full performance.

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