The primary difference between serial and parallel transmission is in the way the data is transmitted. In serial transmission it is sequential whereas, in parallel transmission, it its simultaneous. In the computer world, data is transmitted digitally using bits. In serial transmission, data is sent sequentially where one bit after the other is sent through a single wire. In parallel transmission, data is sent parallel where several bits are simultaneously transmitted using multiple wires. Due to various reasons, which we discuss below, serial transmission has more advantages than parallel tra\
nsmission and hence today serial transmission is followed in most used interfaces such as USB, SATA and PCI Express.
Serial transmission refers to transmission of one bit at a time where the transmission is sequential. Say we have a byte of data “10101010” to be sent over a serial transmission channel. It sends bit by bit one after the other. First “1” is sent and then “0” is sent, again “1” and so on. So, essentially, only one data line/wire is needed for transmission and it is an advantage when cost is considered. Today, many transmission technologies use serial transmission as it has several advantages. One important advantage is the fact that because there are no parallel bits there is no need for synchronization. In that case, clock speed can be increased up to a very high level that a great baud rate can be achieved. Also, due to the same reason,it is possible to use serial transmission for long distance without any issue. Also, since there are no nearby parallel lines, the signal is not affected by phenomena such as cross talk and interference from the neighboring lines, as what happens in parallel transmission.