Serial vs Parallel

Serial vs. parallel transmission simply describes how bits travel from one component to another component across a network. In a computer, parallel transmission is used because distances are short and data must be manipulated quickly. Once outside the PC, serial transmission dominates. Serial transmission is single-file, Indian-style transmission, where one bit follows another down a single pathway as shown in Figure 5-2.

Serial transmission requires one, two, or four wires, depending upon the electrical properties of the signal. In contrast, parallel transmission requires a single wire or path for every bit. This could mean 8 wires, 16 wires, or more, depending upon the width of the pathway (number of bits, 8, 16, 32, or 64). 32-bit CPU chips use 64-bit or 128-bit data pathways internally in PCs. The next step is to 64-bit CPU chips and even wider data pathways.

Serial transmission runs across copper wire, optical fiber, and Radio Frequency (RF) channels in telecommunications networks. Virtually all WANs (data communications) and LANs are serial links. On a PC, the parallel port connecting to a printer is the remaining parallel transmission interface and this will soon disappear when Universal Serial Bus (USB) printers

Serial Bits Parallel Bits Transmissib
Figure 5-2 Serial vs. parallel transmission.

and peripherals take over in the next couple of years. The USB interface uses (as you have already guessed) bit serial transmission.

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