HARD DISKS MOVE FROM 512 TO 4096 BYTE SECTORS

western-digital-wd15eads

Hard disk tracks using 512 byte sectors are becoming harder to handle. The move to the larger 4096 byte sectors have advantages galore.

The WD15EADS is the first disk in the studio that uses the new 4096 sector blocks.

For over 30 years, data stored on hard drives has been formatted into small logical blocks called sectors, with a legacy sector size of 512 bytes. Many aspects of modern computer systems still have design assumptions based on this format standard.

The legacy sector format contains a Gap section, a Sync section, an Address Mark section, a Data section, and Error Correction Code (ECC) section.

The typical track is laid out as:

  • Gap section: The gap separates sectors.
  • Sync section: The sync mark indicates the beginning of the sector and provides timing alignment.
  • Address Mark section: The address mark contains data to identify the sector’s number and location. It also provides status about the sector itself.
  • Data section: The data section contains all of the user’s data.
  • ECC section: The ECC section contains error correction codes that are used to repair and recover data that might be damaged during the reading or writing process.

The Advanced Format standard uses the same number of bytes for Gap, Sync, and Address Mark, but increases the ECC field to 100 bytes. This yields a sectorized format efficiency of 97%. Over time, these format efficiencies pay off, helping to yield higher capacity points while also improving data integrity.

The introduction of 4K-sized sectors had depended heavily on 512-byte sector emulation. This term refers to the process of translating from the 4K physical sectors used in Advanced Format to the legacy 512-byte sectors expected by host computing systems.

The ECC are Reed-Solomon forward error correcting codes which are now widely used with storage to be able to make them relatively error free.