Reasons of hard drive capacity clipping

Hard drive capacity clipping is a phenomenon when available hard drive capacity is less than the capacity advertised by a drive vendor. This incorrect disk size problem can be caused by several reasons, such as mismatched measurement units or various hardware and operating system limitations.

Mismatched measurement units

Before you start figuring out why your computer doesn't see the full disk size, you should know that the size declared by the hard disk manufacturer is always greater than the size the system sees. This is because the fact that the hard disk manufacturers specify the disk size in "decimal" MB/GB/TB, and the computer operates the "binary" unit. Thus, if your hard disk manufacturer declares that the disk size is 200 GB, in Windows Explorer you see 186 GB as the total size of all partitions on the disk (as discussed, for example, in this thread on Tom's Hardware forum).

  • 1 "decimal" GB = 1 000 000 000 bytes
  • 1 "binary" GB = 1024*1024*1024 = 1 073 741 824 bytes

Thus, 200 000 000 000 / 1 073 741 824 = 186 GB.

Additionally, a filesystem reserves some disk space for its own purposes, further reducing the available space.

However, if the declared and the actual sizes differ by more than the difference related to the "binary"/"decimal" unit, most likely, you are dealing with a phenomenon called "capacity clipping".

Other possible reasons of capacity clipping
  • Old motherboards may have a limit on the size of the connected drive. In this case, the BIOS either does not show the drive at all, or shows it as 128GB.
  • Windows 2000 and earlier versions and Windows XP without Service Pack don't recognize the disks larger than 128 GB (binary) or 137 GB (decimal). So those logical disks which are beyond the limited area of the physical disk will be unavailable. Note that if the boot volume (containing Windows installation files) is larger than 128/137 GB, then the computer won't start up.
  • Most of the hard drives have jumpers designed to limit the disk capacity for compatibility with older computers. The limitations can be either up to 2 GB, or up to 32 GB, or up to 128/137 GB. In this case, BIOS will detect the drive and show the clipped capacity set by the jumper.
  • The disk can be configured by special software in such a way to show less capacity than it actually has. This feature is called HPA ("Host Protected Area"). For example, on some Hewlett-Packard laptops a copy of Windows installation files is written at the end of the disk to be used in the "Restore to factory condition" function. If HPA is used, BIOS will show the clipped capacity as configured by HPA.

Anyway, if you eliminate the causes of "capacity clipping" (e.g., install Service Pack for Windows XP), then after a restart the disks will be recognized automatically. In most cases all these newly recognized disks will be in good condition and with correct sizes; therefore, no special data recovery activity is required.

How to fix hard drive capacity clipping

  1. If you deal with the old motherboard (manufactured before 2007), then sometimes the problem can be solved by upgrading to the newer BIOS version. To do so, you need to visit the motherboard vendor web site. Note that the modern motherboards (manufactured after 2007) don't have such limitation.
  2. As for Windows XP without Service Pack, you need to install the latest updates (the latest Service Pack), set the EnableBigLba registry value to 1 in

    HKEY_LOCAL_MACHINE\​System\​CurrentControlSet\​Services\​Atapi\​Parameters\

    and then restart the computer. For more information please refer to Microsoft Knowledge Base article 303013.

  3. If the disk has been recently removed or has just been brought in from another computer, then it makes sense to check the jumpers on the disk. The jumper block is located next to the power and data connectors on the disk. Usually you can find the scheme of various jumper block options printed on the top cover of the disk; it looks like this example:
    Sample hard drive jumper settings diagram.
  4. If the disk size was limited by software (HPA), then to remove this limitation you can use the HDD Capacity Restore utility, (c) 2007 Atola Technology, http://hdd-tools.com/. Note that when you fix the disk size using this utility, the data contained on the disk remains intact, and no data recovery is needed. Click here to download HDD Capacity Restore.
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