Serial
Serial data transfer is when all the bits are lined up in single file and sent in one line down a transmission medium. This approach makes a lot of sense if you are requiring the data transfer to travel over a long distance. It is not very efficient because all the buses on your motherboard are either 32 bit or 64 bit so they are not serial.ParallelParallel data transfer is when the bits are sent in batches down several lines at the same time. This type of data transfer was created in order to speed up the data transfer, especially when large amounts of data have to be transferred. This type of approach was used to connect printers to computers for a very long time. It does provide a greater data transfer rate than serial but it does not work so well over larger distances and takes quite a lot of effort to get the data organized for transfer and then reassembled at the other end.Since the advances in technology have allowed the frequency of buses that transfer data off a motherboard to be significantly increased serial transfer has been preferred in order to avoid the complexities of organizing the data for parallel data transfer.All computer networking is serial, USB and Sata have all used a serial link at a very high frequency to significantly improve the overall data transfer rate.