Advanced Format - Harddisk

Advanced Format changes a hard drive's sector size from 512 bytes (the standard for the past three decades) to 4K

For more information:

http://hothardware.com/Articles/WDs-1TB-Caviar-Green-w-Advanced-Format-Windows-XP-Users-Pay-Attention/

http://www.anandtech.com/show/2888

Advanced Format - Harddisk