In data transmission, parallel communication is a method of conveying multiple binary digits (bits) simultaneously using multiple conductors. This contrasts with serial communication, which conveys only a single bit at a time; this distinction is one way of characterizing a communications link. The basic difference between a parallel and a serial communication channel is the number of electrical conductors used at the physical layer to convey bits. Parallel communication implies more than one such conductor. For example, an 8-bit parallel channel will convey eight bits (or a byte) simultaneously, whereas a serial channel would convey those same bits sequentially, one at a time. If both channels operated at the same clock speed, the parallel channel would be eight times faster. A parallel channel may have additional conductors for other signals, such as a clock signal to pace the flow of data, a signal to control the direction of data flow, and handshaking signals. Parallel communication is and always has been widely used within integrated circuits, in peripheral buses, and in memory devices such as RAM. Computer system buses, on the other hand, have evolved over time: parallel communication was commonly used in earlier system buses, whereas serial communications are prevalent in modern computers. Examples of parallel communication systems Internal buses: memory bus, system bus, and front-side bus IBM System/360 Direct Control Feature (1964). Standard System/360 had an eight-bit wide port. The process-control variant Model 44 had a 32-bit width. Legacy computer peripheral buses: ISA, ATA, SCSI, PCI, and the once-ubiquitous IEEE-1284 / Centronics "printer port" Laboratory Instrumentation bus IEEE-488 (see more examples at computer bus) Comparison with serial links Before the development of high-speed serial technologies, the choice of parallel links over serial links was driven by these factors: Speed: Superficially, the speed of a parallel data link is equal to the number of bits sent at one time times the bit rate of each individual path; doubling the number of bits sent at once doubles the data rate. In practice, clock skew reduces the speed of every link to the slowest of all of the links. Cable length: Crosstalk creates interference between the parallel lines, and the effect worsens with the length of the communication link. This places an upper limit on the length of a parallel data connection that is usually shorter than a serial connection. Complexity: Parallel data links are easily implemented in hardware, making them a