In measuring data transmission speed, a terabit is one trillion binary digits, or 1,000,000,000,000 (that is, 1012) bits. A terabit is used for measuring the amount of data that is transferred in a second between two telecommunication points or within network devices. For example, several companies are building a network switch that passes incoming packets through the device and out again at a terabits-per-second speed. Terabits per second is usually shortened to Tbps.
Although the bit is a unit of the binary number system, bits in data communications have historically been counted using the decimal number system. For example, 28.8 kilobits per second (Kbps) is 28,800 bits per second. Because of computer architecture and memory address boundaries, bytes are always some multiple or exponent of two.