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8 512e and 4Kn Disk Formats
Figure 2 Potential read sequence for 512-byte emulation
The process of reading the 4K block of data and reformatting to the specific 512-byte emulated sector
requested by the host computer is performed in the drive’s DRAM memory and does not measurably
impact performance.
A write process will be more complicated, particularly when data the host computer attempts to write is a
subset of a physical 4K sector. In these cases, the hard drive must first read the entire 4K sector containing
the targeted location of the host write request, merge the existing data with the new data, and then
rewrite the entire 4K sector as shown in Figure 3. The fundamental reason for this is that the drive cannot
write just a portion of the 4K sector, but can only write the entire sector at once.