Why is Serial communication preferred over Parallel ?

All technologies are migrating onto “serial” instead of parallel, although parallel is about 10 times faster than serial data communication. Eg:

• SATA over Parallel ATA [IDE]
• The SCSI interface is also being transformed into serial.

What makes the parallel communication faster is that multiple bits are transmitted simultaneously, whereas bit by bit transmission occurs in serial.

The serial communication may be faster than the parallel one, provided the bits leave the transmitting device at a much higher speed. An example of such is the ATA 2 Serial port that however serial can reach a transfer rate of up to 300 MB/s, while the traditional IDE port [P-ATA] goes to 133 MB/s at the most.

The complications of using Parallel data transfer is that that many wires are required as the width of bus. E.g : A 32 bit PCI bus would have 32 wires and the controls are required for each.

In serial communication, just two wires will do the mojo. Also, as the speed of data transfer increases, the e.m disturbances also increases, making parallel data transfer very difficult.

Another problem with parallel commu. is that the bits may not reach the destination at the same time. The various reception time of the several bits makes the device wastes time having to wait for all the bits to arrive, which may represent a significant fall in performance.

Finally, parallel data tx. is semi duplex or half duplex, whereas serial data tx. is full duplex. In the serial communication, since it only uses two wires, the manufacturers usually make four wires available, two for the transmission and two for the reception of data. That makes it possible for the simultaneous transmission and reception of data. Such architectural difference alone makes the serial communication about twice as fast as the parallel communication.