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In reference to computer storage media, the native capacity of a certain device or drive is the amount of space that actually is physically present on the drive or device. The distinction of a native capacity, as opposed to other measurements of capacity, is made in situations in which the information that is written to a device usually is compressed or otherwise processed before writing, giving the device a higher compressed capacity. For systems that employ compression hardware or software, such as high-end tape drives, the native capacity usually is not listed as the size of the drive; instead, the compressed capacity is given. Different types of files compress at different ratios, however, so native capacity is a way to see how much information a drive can hold in a worse-case scenario of zero compression for all files.
Many times, the amount of space available on a storage device that uses compression is given as the amount of data that can be stored after being compressed. Should a high number of files that do not benefit from compression be stored to the disk, then the compressed capacity will diminish. In situations in which large numbers of already compressed files, executables or encoded images will be stored, the native capacity is a better judge of how much information a particular drive will hold.
Within a storage device, the native capacity listed is not necessarily the amount of space that actually can be used for data. Most times, when a file or multiple files are stored on a device, information about the size and name of the file also is stored, usually in a special area of the disk itself. This means that, for every file that is written, a certain amount of extra of disk space is required so the file can be accurately reconstructed. Overall, this can reduce the amount of usable space on a disk by a measurable amount.
Another distinction to be made when judging native capacity is that there actually are two forms of measurement. The most basic is called a decimal measurement and is fairly straightforward, being just the actual amount of space that is available. The second type of measurement is known as binary and deals with binary math that regularly is used by computers, operating systems and file systems. If a drive has 1 terabyte of native capacity, this could mean 1,000 decimal gigabytes or, alternately, it could mean just more than 931 binary gigabytes, although most manufacturers will make the distinction somewhere in the literature for a device.