Other storage media characteristics

The most common storage media characteristics are

Capacity

is given in byte (one byte = 8 bit = one octet). Note that the terms kilo-, mega-, giga-, and terabyte are used ambiguously because they can be based on the decimal (kilo = 1000) or the binary system (kilo = 1024 = 2^10).

Speed of access

is measured in seconds and refers to the time needed to access a given memory location. In mechanical systems, e.g. disk or CD-ROM, the access time is largely determined by the seek time, i.e. the time needed to access a specified track and find a particular memory location.

Data rate

is given in bit or byte per second and refers to the amount of user data that can be transferred within a period of time. Raw data rate refers to the total amount of data transferred, i.e. administrative data exchange with the device controller plus the user data. In general, the raw data rate is much higher than the user data rate.

Cost

of storage is determined by the cost of the storage device, the storage medium (for interchangeable media like tapes, hard disk cartridges, etc.), and the cost of maintenance. The cost of medium can be given in absolute or relative terms, e.g. cost per megabyte.

Location

of a storage device is either internal, i.e. built into a computer, or external, i.e. a separate device. Internal devices occupy slots in the bus and require that there is sufficient space and power supply. External devices attach to the computer via peripheral connectors, e.g. SCSI-ports or PCMIA slots, and usually they have their own power supply. In principle both external and internal devices can be addressed through the same protocol, e.g.\ SCSI; however, different interfaces are very common, depending on the quality of the hardware and the bus architecture.