As your main storage unit, your hard drive must be big enough to hold your operating system, applications, and growing collection of videos, games, photos and music files, as well as all the other data you accumulate over the years.

With applications and file sizes growing in leaps and bounds, a hard drive that is big enough now might not be big enough in a year or two. For example, each new generation of digital camera offers higher-resolution images than its predecessor, and these images require more storage space.

Defining the Storage Capacity of Your Hard Drive

Hard drive manufacturers define 1 Gigabyte (GB) to mean 1,000,000,000 bytes in powers of 10 (109 bytes). The computer operating system (OS), however, defines 1 GB as 1,073,741,824 bytes in powers of 2 (230 bytes). Because a Gigabyte as defined by the OS is larger than a Gigabyte as defined by the hard drive manufacturers, the OS will show the same hard drive to have fewer Gigabytes of storage capacity than that given by the hard drive manufacturer. In fact, the hard drive has the same storage capacity under either definition.

As a practical example, the difference in definitions means a hard drive manufacturer’s 40 GB hard drive would be listed as having 37.2 GB by the OS. However, the actual available storage capacity reported by the OS will be even less than the total storage capacity of 37.2 GB for the reasons explained in the following section.

Once Installed on Your Computer, Your Hard Drive Will Have Its Storage Capacity Reduced by Formatting and the Storage of Other Content Used to Run Your Computer.

In order for a hard drive to be compatible with an operating system, the hard drive must be formatted for use by the operating system. Formatting a hard drive requires using a portion of the hard drive’s capacity and thus reduces available storage capacity from the unformatted total storage capacity. Available storage capacity will also be reduced if operating systems, applications, or media content are pre-installed on the hard drive.