FAQ

Terminology
Sector – An atomic unit of data transfer size from/to a hard Disk Drive
LBA (Logical Block Address) – An atomic unit of hard disk drive (HDD) sector address (location).
Physical Sector – Sector size at the HDD media level, normally is 512 bytes
Physical LBA – LBA layout on HDD media level, each LBA has the Physical Sector size
Logical Sector – Sector size defined at the host–to-disk drive interface. Normally the same size as
Physical Sector unless the HDD is emulating.
Logical LBA – LBA layout at host-to-disk drive interface, each LBA has the Logical Sector size.
Frequently Asked Questions
1. What is a 4K sector HDD? How is it different from standard 512 bytes sector
HDD?
4K sector HDD is a new generation HDD whose physical sector is 4K bytes. As HDD areal density
increases, the footprint of each physical sector shrinks. However, since the natural contamination (dust,
particulate, etc.) remains about the same size, the ratio between the footprint of the media defect and the
physical sector is increasingly larger. It requires more embedded ECC per each physical sector to maintain
the published sector error rate. By increasing the physical sector size to 4K bytes, the ratio is reduced
therefore the error correction code (ECC) burden per physical sector is also reduced. The larger physical
sector not only improves format efficiency but also improves media defect correction ability and signal-
to-noise (S/N) design margin. Current shipping HDDs are based on 512 byte physical sector and logical
sector.
2. What is 4K native HDD and what is 512 emulation (512e) HDD?
There are two models of 4K sector HDDs:
1. 4K native HDD is a 4K sector HDD whose logical sector is the same as physical sector. Therefore
the logical sector size is 4K bytes instead of the legacy 512 bytes. This is incompatible with legacy
BIOS and Operating Systems.
2. 512 emulation (512e) HDD is a 4K sector HDD whose logical sector is 512 bytes (not matching with
physical sector). It no longer has a one-to-one relationship between physical sector and logical
sector. Instead, one 4K physical sector consists of eight logical 512 bytes sectors (4K bytes = 8 *
512 bytes). This is done to make the 512 emulation HDD compatible to legacy BIOS and Operating
Systems.
5 4K Sector HDD FAQ