Bitdensity

Bitdensity is a general term used to describe the amount of information, measured in bits, that can be encoded per unit of a given resource. It is not a single standardized quantity; rather, it encompasses various measures that share the same idea of information content divided by a resource such as area, length, time, or bandwidth. Depending on the domain, the unit may be areal density (bits per square unit), linear density (bits per unit length), temporal density (bits per unit time), or spectral efficiency (bits per second per hertz).

In storage technology, areal density is a common instantiation, expressed as bits per square inch or per square millimeter, used to compare the capacity of disks, tapes, and flash memory.

In imaging and media, bit density can refer to bits per pixel (bpp), indicating how many bits are used to represent each picture element, often influenced by compression.

In communications, bit density can denote the data rate divided by the available bandwidth, i.e., spectral efficiency, measured in bits per second per hertz.

Calculation, in general, is D = Nbits / R, where R is the chosen resource. For example, 1 terabit stored on 1 square centimeter yields approximately 1e12 bits per cm^2; a 4 Mbps video over a 22 MHz channel gives about 0.18 bits per Hz.

Limitations: Because the denominator is not fixed, bitdensity is a comparative metric. Values depend on encoding overhead, error-correcting codes, and formatting.

See also: data density, areal density, linear density, spectral efficiency, bits per pixel, information density.