Serial versus parallel
Serial data is probably the most ubiquitous type of data transfer. It is how we as humans are accustomed to communicating. You are doing it right now as you read this. Serial communication simply means that data is transmitted and received one unit at a time (as opposed to several units of data being transmitted in parallel).
In the case of reading this book, your eyes are processing each word by scanning each line of text from left to right, then proceeding back to the beginning of the next line and continuing. You are processing a serial stream of words that are used to communicate some thoughts and ideas. Conversely, imagine if you could read the book several lines at a time. This would be considered parallel data transfer and it would be awesome!
The unit of data that is used in computing is the bit, which is a binary representation for on or off, more commonly 1 or 0.
Parallel data transfer was popular in the early years of computing since it allowed...