Hard drive shows less capacity than expected

Here I mostly talk about older hardware, items one regrets not having tossed into the bin.

The capacity limit on a hard drive did exist because the older LBA standard only allowed 28 bits for a sector address. Hence, there was a limit of 2^28 sectors on a drive. With 512 bytes per sector, this works out to 268435456 sectors, or 137,438,953,472 bytes, which equals exactly 128 gigabytes.

Note that 128 GB (137,438,953,472 bytes) is in fact slightly above 137 billion bytes. The hardware makers, unlike software makers, use decimal units when speaking about the hard drive size. Because of this, drive manufacturers can advertise an imaginary 128GB hard disk as having size of 137GB (see The difference between hard drive and file system size).
One can encounter a 128GB limit because the mainboard is badly old (something 2002-ish), or when using an OS massively not up to date (similar to Windows 2000 or Windows XP prior to SP2).
The corrective actions include

  • Flashing the latest available motherboard BIOS. This may or may not work, depending on the specific motherboard.
  • Updating the operating system. If all other components are up to speed, that usually solves the issue.

Most often, the reduction in capacity results from an old hardware or software, which is not compatible with new hard disks, there is one notable exception – the Host Protected Area, or HPA in short (discussed in my previous post).
The HPA is a feature of a hard drive allowing the OS hide a part of the capacity of the hard drive. HPA was implemented to allow for backward compatibility, so that one can use hard drive in an old PC which does not support large disks. If activated unintentionally, the HPA fools the OS to behave like the hard disk is smaller than it should be.
If this condition is not desired, you can reset the HPA, usually with vendor-supplied software.

HPA in laptops as an alternative choice to a recovery disc

Vendors of laptops may give a recovery disc or may not. Makers who don’t give the CD to their users generally put the original Windows OS installation to the special partition along with a tool which is capable of deploying this OS installation back to the drive.

Such a partition containing the OS is placed in the end of the drive and hidden from the Windows by the means of HPA (Host Protected Area, described nicely e.g. at www.disk-space-guide.com).

The recovery process for a laptop with Host Protected Area can be the following:

  • you press certain keys during startup sequence
  • BIOS discards HPA limitations
  • Windows is loaded off the appeared recovery partition
  • a special tool starts from this partition. This tool formats the drive and copies the factory Windows installation to the disk.

When the recovery is complete, HPA is set back. After this process is complete the laptop is as good as new from the store, software-wise.