What is concurrency?

At a basic level, concurrency stands for more than one activity happening at the same time. We can correlate concurrency to many of our real-life situations, such as eating popcorn while we watch a movie or using two hands for separate functions at the same time, and so on. Well then, what is concurrency in a computer?

Computer systems were enabled to do task switching decades ago, and multitasking operating systems have been in existence for a long time. Why is there renewed interest in concurrency all of a sudden in the computing realm? The microprocessor manufacturers were increasing computing power by cramming more and more silicon into a processor. At a certain stage in the process, they could not cram more things into the same area as they reached fundamental physical limits. The CPUs of those eras had a single path of execution at a time and they were running multiple paths of instructions by switching tasks (stream of instructions). At the CPU level, only one...