Zone bit recording

Zone Bit Recording (ZBR) is used by disk drives to store more sectors per track on outer tracks than on inner tracks. It is also called Zone Constant Angular Velocity (Zone CAV or Z-CAV or ZCAV).

On a disk consisting of concentric tracks, the physical track length increases with distance from the center hub. Therefore, holding storage density constant, the track storage capacity likewise increases with distance from the center.ZBR is a compromise between CLV (which packs the most bits onto a disk, but has very slow seek times) and CAV (which has faster seek times, but stores fewer bits on a disk).

To implement ZBR, a drive's controller varies the rate at which it reads and writes - faster on outer tracks. Alternatively, the disk rotation rate could be slowed, as was done by the original Apple Macintosh floppy disk.

One side effect of ZBR is the raw data transfer rate of the disk when reading the outside tracks is much higher -- in some disks, about double -- the data transfer rate of the same disk when reading the "inner" (closest to the hub) tracks. [ [http://www.storagereview.com/guide/tracksZBR.html "Zoned Bit Recording"] ]

Products that use ZBR/ZCAV

*Commodore 1541 floppy disk
*Apple Macintosh 400K/800K floppy disk
*DVD-RAM
*HD DVD-RW (note: not HD DVD-ROM or HD DVD-R)
*Most hard drives since the 1990s

ee also

* Zoned constant linear velocity
* constant linear velocity