Advanced Format hard drives use 4 KiB (4096 byte) sectors, instead of the 512 byte sectors used for a very long time. This change has significant impacts on hardware, BIOS/UEFI firmware, operating systems, partitioning tools, boot loaders and even the performance of applications.
One key change is that sector size is now split into two concepts: logical sector size (seen by the OS by default) and physical sector size (visible with extra support in OS and tools). Early Advanced Format drives keep 512 bytes as the logical sector size (termed 512 emulation) with 4 KiB as the physical sector size - but some drives pretend to have a 512 byte physical sector size while actually using 4 KiB internally.
Resources:
- Introduction to Advanced Format from Anandtech
- Advanced Format Wikipedia article - good overview across operating systems
- Linux - 4 KiB sector issues from Kernel.org
- LWN article
