1. Parallel and Serial Connections

For most of the history of the personal computer, external and internal devices have communicated to each other through parallel connections. However, given the limitations of parallel connections, engineers began to develop technology based on serial connections, since these have greater data transfer rates, as well as more reliability.

A serial connection is a wire or set of wires used to transfer information from the CPU to an external device such as a mouse, keyboard, modem, scanner, and some types of printers. This type of connection transfers only one piece of data at a time. The advantage to using a serial connection is that it provides effective connections over long distances.

A parallel connection uses multiple sets of wires to transfer blocks of information simultaneously. Most scanners and printers use this type of connection. A parallel connection is much faster than a serial connection, but it is limited to shorter distances between the CPU and the external device than serial connections.

The best way to see the difference between parallel and serial connections is to imagine the differences between a freeway and a high-speed train line. The freeway is the parallel connection—lots of lanes for cars. However, as more cars are put onto the freeway, the slower each individual car travels, which means more lanes have to be built at a high cost if the cars are to travel at high speed. The train line is the serial connection; it consists of two tracks and can only take two trains at a time. However, these trains do not need to deal with traffic and can go at higher speeds than the cars on the freeway.

As CPU speeds increased and engineers increased the speed of the parallel connections to keep up, the main problem of parallel connections—maintaining data integrity at high speed—became more evident. Engineers began to look at serial connections as a possible solution to the problem. This led to the development of both SATA and PCI Express, which, by using serial connections, provide high data transfer rates with less materials used and no data loss.

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