What is Zoned Bit Recording (ZBR)? (Explained)

What is Zoned Bit Recording (ZBR)?

Zoned Bit Recording, or ZBR, refers to the particular method of recording data that allows increasing the available space on the hard drive by adding more sectors on each of the outer tracks on the hard drive.

From a technical point of view, this technology utilizes the remoteness of the center of the hard disk drive from the sectors on the outer tracks that offers more space and allows storing more data on them.


  • Also referred to as Zone CAV or Z-CAV, Zoned Bit Recording is the process in which the disk space is broken into several different zones, each of which contains several thousand tracks, depending on its location on the platter.
  • ZBR helps in storing more data on the outer tracks, and coupled with the constant speed of the spindle, it preserves the density of recording by keeping it constant all through the magnetic disk surface.
  • Since there are more sectors on the outer tracks created by ZBR than in the inner ones of the disk, more data is stored in these areas. This eventually increases its data storage capacity compared to a platter of the same size.
  • ZBR allows more efficient use of storage space of the disk on a hard drive without affecting the reliability of the data stored on it adversely. In fact, when used with other magnetic recording methods, it adds record density.
  • Most of the hard disk drives designed after the 1990s use Zone Bit Recording process to store data on them. In addition to that, a few floppy disks also used this technique just as the DVD-RAMs do.

Understanding Zoned Bit Recording (ZBR)

What is Zoned Bit Recording (ZBR)


Zoned Bit Recording increases the storage capacity of a hard disk drive by assigning more sectors per track on the outer region of the disk. This specific technique is also known by different names such as:

  • Multiple-zone recording
  • Zone recording

In this process, the tracks on the disk are grouped into several different zones depending on their respective distances from the center of the disk or spindle. Every zone is allotted a specific number of sectors per track.

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This means that, as you move outward, the number of sectors is more than that on the inner tracks.

BIOS Perspective

Looking from a different perspective, the Zoned Bit Recording technique also had some notable effects on the Basic Input Output System (BIOS) settings, especially for the Integrated Drive Electronics (IDE) and Advanced Technology Attachment (ATA) hard disk drives.

Typically, these drives allowed the specification of only one number for the sectors on every track.

However, since all modern hard disk drives use the ZBR technique, they typically do not have only one number of sectors on every track across the disk. These drives normally use logical geometry for the purpose of the BIOS setup.

Normally, the IDE hard drives with a capacity of up to 8.4 GB tell the BIOS they have 63 sectors per track and then decipher internally to the real geometry.

However, the modern drives typically do not use 63 sectors on any of the tracks. In fact, all of them use much less than that.

In general, the hard drives with a storage capacity in excess of 8.4 GB cannot have their specifications represented through the IDE BIOS geometry parameters.

This is because the standard BIOS restriction is 8.4 GB, and therefore the drives will always have 63 sectors on each track as a dummy geometry specification. This will be accessed with the help of logical block addressing.

Ideally, over time, all these complications along with the storage capacity and speed of the hard disk drives have improved due to better utilization of the larger outer tracks on the disks, which is the result of Zoned Bit Recording.

Utility for the Drives

The technique is very useful in two specific ways, such as:

  • It allows storing more bits on the outer tracks in comparison to the inner ones.
  • It uses the inner zoning to set the read/write rate, which is the same for all other tracks.

This eventually ensures that the disks have a much higher data density on the same disk and also influences other particular performance aspects of the hard disk drive.

One of the most noteworthy improvements in the performance of the hard disk drives is in the rate of raw data transfer, which is sometimes referred to as the media transfer rate.

This means less time is taken while reading the data on the outer cylinders than those on the inner ones. This is due to two particular reasons, such as:

  • There is more data stored in the outer cylinders.
  • The angular velocity of the disk platters is constant, irrespective of which track is being read.
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Utility for the Drive Controllers

Zone Bit Recording technology helps the controllers of the modern hard disk drives to handle the changed and more complex arrangements of tracks, which was quite a primitive affair in the earlier drives.

Ideally, the standard for the hard disk drives was to have an equal number of sectors on every track. Based on this standard, the earlier hard disk drives had seventeen sectors on each track.

However, the tracks are typically concentric circles and therefore the ones on the outer side of the platter were larger than those on the inside, or close to the center, being almost half their circumference.

However, due to the design constraints, the given technology, and the standard to abide by, this is what happened in the early hard disk drives:

  • The inner circles were packed with bits as tightly as practically possible, according to the technology.
  • The outer circles, for similar reasons, were loosely packed with data and therefore the bit density was lower in that case.

This means that the outer tracks were typically underutilized. This resulted in wastage of storage space, because, theoretically, the outer tracks could hold a lot many more sectors than it actually did, given the equivalent linear bit density restrictions.

With the use of the Zoned Bit Recording technique, such wastage of storage space was eliminated in the modern hard disk drives, and overall, it increased the efficacy of the drive controllers.

Utility for the Operating Systems

The fact that ZBR allows storing more data on the outermost tracks with much higher data transfer rates, also helps the operating system a lot in its functioning.

This is due to two specific reasons, such as:

  • The tracks on the hard disk drives, as it is done in the floppy disks as well, are typically numbered from the outer ones, continuing inward.
  • The operating system usually fills the tracks with the lowest number with data first, which is where it normally stores its own files at the time of initial installation of an empty hard disk drive.

This means that the operating system can store all the necessary files on these outer sectors to access them faster.

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Since the launch of Zoned Bit Recording, several products have used this technique to store data on them. Though the floppy disks are more or less extinct, the others are not. Some of these products are:

  • The Commodore 1541 floppy disks – These disks combine ZBR and Group Code Recording (GCR) for sectors 17 to 21 sectors at 256 bytes in four different writing speed zones.
  • Sirius 1/Victor 9000 floppy disks – These disks combine ZBR, GCR, and Zoned Constant Linear Velocity (ZCLV) for sectors 11 to 19 at 512 bytes in nine different rotation speed zones.
  • Apple Macintosh 400K and 800K floppy disks – These disks combine ZBR and GCR as well.

In addition to that, the Digital Versatile Disc – Random Access Memory (DVD-RAM) and most of the hard drives from the 1990s onwards use Zoned Bit Recording to store data.

Zoned Bit Recording Vs Logical Block Addressing

  • Zoned Bit Recording makes the layout of the disk much more complex. On the other hand, Logical Block Addressing, being a linear addressing scheme, does not.
  • The Zoned Bit Recording process allows maximizing the tracks on the hard disk drives to increase the data storage capacity. On the other hand, Logical Block Addressing is a scheme that specifies the location of data blocks stored on hard disk drives.
  • In the Zoned Bit Recording process more sectors are placed on each zone on the outer tracks of the hard disk drives than on the inner tracks. On the other hand, in the Logical Block Addressing scheme each data block is given a unique integer index for storage.


So, now you know that Zoned Bit Recording is a specific data recording process on a hard drive where the number of sectors on each track is not constant across the platter of the disk.

Usually, the tracks that are nearer the center have less sectors than those away from it, and so have more space to store more data.

About Puja Chatterjee

Puja ChatterjeePuja Chatterjee is a technical writer with extensive knowledge about computers. She graduated from BIMS. Her expertise includes technology writing and client relationship management gained through over 12 years of experience. Follow Her at Linkedin.

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