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Zoned constant angular velocity (ZCAV) is a disk-recording arrangement that groups tracks into zones, with a different sectors-per-track count in each zone. In hard drives, outer zones can store more sectors per track because their tracks have a longer circumference. The approach uses that geometry to increase capacity, but transfer rates can vary with the sector address or head position.
How ZCAV works on a hard drive
A hard drive records data on concentric tracks. With ZCAV, tracks are grouped into zones, and tracks within a zone use the same number of sectors per track. The sectors-per-track count can differ between zones.
Outer tracks have a longer circumference than inner tracks. Assigning more sectors to tracks in outer zones makes use of that additional space, which is the capacity rationale described by Rodney Van Meter in “Observing the Effects of Multi-Zone Disks”, presented at the USENIX Annual Technical Conference in 1997.
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| Method | How it handles rotation and tracks | What happens across disk positions |
|---|---|---|
| CAV | Maintains constant angular velocity and, in the cited hard-drive comparison, the same number of sectors per track. | Does not use ZCAV’s varying sectors-per-track zones. |
| CLV | Changes rotational speed to maintain constant linear velocity. | Uses a different approach from ZCAV’s zoned sectors-per-track layout. |
| ZCAV | Maintains angular velocity while grouping tracks into zones with different sectors-per-track counts. | Transfer rate can vary by sector address or head position. |
The comparison describes the hard-drive context in Van Meter’s paper. ZCAV and ZCLV are also listed as separate velocity-mode values in ECMA-280, an optical disk cartridge standard; terminology in that standard should not be treated as a complete description of every hard-drive implementation. See ECMA-280, 1st edition.
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Does ZCAV provide a uniform transfer rate?
No. Zoning can increase capacity, but transfer rate may vary with where data is located or which head position is involved. Van Meter’s 1997 paper reported a roughly 25% peak transfer-rate drop depending on head position in its analysis and measurements on a BSD Fast File System. That result belongs to the paper’s specific context; it is not a universal benchmark for current drives.
Is ZCAV a feature you can choose when buying a drive?
The cited technical paper discusses ZCAV as a hard-drive recording arrangement, but it does not establish that current drive models advertise ZCAV or let buyers select it as a feature. Treat ZCAV primarily as a way to understand disk layout and possible position-dependent transfer behavior, not as a guaranteed product specification.
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