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Zone bit recording (ZBR), also called zoned bit recording, is a hard-disk layout that groups tracks into zones and stores more sectors on each outer track than on an inner one. Since outer tracks have a longer circumference, this arrangement uses more of the platter’s recording area and can deliver higher sequential transfer rates in outer zones.
How zone bit recording works
A hard-disk platter has concentric tracks at different distances from its center. A track farther from the spindle is longer because it follows a larger circle. ZBR divides tracks into zones and assigns more sectors to tracks in zones nearer the platter’s outside edge than to tracks nearer the center.
A sector is a subdivision of a track used to store data. Giving longer outer tracks more sectors lets the drive use their additional circumference instead of storing the same number of sectors on every track. Thomas M. Ruwart describes the result in section 8.1 of Disk Subsystem Performance Evaluation: “This allows for more efficient utilization of the recording area and hence greater overall capacity.”
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Why outer tracks can transfer data faster
When a drive rotates at a constant rate, each revolution brings a track past the read/write head. Because an outer track can contain more sectors, more recorded data passes the head during one turn than on an inner track. The sequential transfer rate can therefore be higher in outer zones than in inner zones.
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The advantage depends on the physical location of the data. It describes sequential data transfer, not a general guarantee that every task will be faster. The available sources do not establish a universal percentage for the difference; it varies by drive.
Zone bit recording compared with a uniform track layout
| Feature | Zone bit recording | Uniform sectors-per-track layout |
|---|---|---|
| Sectors per track | More sectors are assigned to outer tracks than inner tracks. | The same number of sectors is assigned to every track. |
| Use of platter area | Uses the longer circumference of outer tracks to store more data. | Does not increase the sector count on longer outer tracks. |
| Sequential transfer by location | Can be higher in outer zones at constant rotational speed. | No outer-zone advantage follows from a varying sector count, because the count is uniform. |
What ZBR does—and does not—tell you
ZBR explains how a hard disk arranges data on its recording surface. It can help explain why sequential transfer rates vary depending on where data is located. The term alone does not establish a specific drive’s performance, a guaranteed application speedup, or its seek time or latency. Those details require evidence about the particular drive and workload.
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