Western Digital is among the companies building hard drives that store more data in the same advertised capacity, thanks to a new technology.
Advanced Format Structure, as WD calls it, reduces the number of "sector gaps" needed to sync the hard drive and correct for errors. As PC Perspective explains, the previous structure, which has been in use for over 30 years, contained just 512 Bytes of data per sector gap, while Advanced Format Structure has larger physical sectors containing 4096 Bytes of data each. If you don't follow, this image explains the basic idea:
As you can see, far less of the drive is used for sync and error correction -- 10 percent, by WD's estimates. Also, error correction actually improves by 50 percent, even though there's less space dedicated to it, thanks to the use of larger error correction code words.
Because most computer systems are still based on the 30-year old 512-Byte system, Advanced Format still emulates sectors of 512 Bytes each. It just reduces the number of gaps needed for those extra, space-consuming functions. For this reason, however, Windows XP will still have trouble reading drives with greater than 2 TB capacity, as they have more sectors than the operating system can handle.
Other downsides? None, unless you're using an older operating system such as Windows XP or cloning drives. In those cases, there's a utility required to align the drive properly.
A white paper by WD (PDF) says the industry as a whole is adopting Advanced Format. There are a few factors that could contribute to a hard drive holding less data than advertised, such as operating system software and specifications in binary, so anything that helps alleviate this problem is welcome.
