Hardware Reference
In-Depth Information
As you can see, the 4K sector (aka Advanced Format) layout uses the same number of
bytes for the sector header as modern 512-byte sectored drives, but it increases the size
of the ECC field to 100 bytes. Even with the larger ECC required to maintain the stand-
ard error rate, this yields a sector format efficiency of 97.3%—almost a 10% improve-
ment. Because of the eight times larger data field, this will also allow further increases
in ECC without dramatically reducing the overall efficiency.
Figure 9.4
shows the format
efficiency improvement from 512-byte sectors to 4K sectors.
Figure 9.4
Format efficiency improvement from 512-byte sectors to 4K sectors.
Although 4K sectors may sound like a simple solution, this transition has many issues.
The main problem is that the 512-byte sector format has been so ingrained into PC oper-
ating systems (OSs) and other software that changing it causes tremendous compatibility
problems. The interim solution to this problem was to have 4K sector drives use internal
emulation to act at the interface level as if they are 512-byte sector drives, a format that
is called 512e (for 512 emulation) in the industry. But even with emulation, there can be
problems.
Consider what happens when a program writes a single sector to a disk. If the drive is a
standard 512-byte sector drive, the one sector is written quickly and efficiently. However,
if the drive is a 4K sector drive that is
emulating
a 512-byte sector drive (512e), the drive
