In simpler times, computers had only one CPU and this marginalized the need for concurrency. Hardware manufacturers successfully found ways to make CPUs faster, and this made single-threaded programs faster. But eventually, this had a diminishing return, and manufacturers found they could increase computational power by putting multiple CPUs in a device. From desktops and laptops to servers and smartphones, most hardware nowadays sports multiple CPUs, or cores.
For developers, this is a major disruption in building software and how coding is done. Single-threaded software is easier to code and works fine on a single-core device. But a single-threaded program on a multi-core device will only use one core, leaving the others not utilized. If you want your program to scale, it needs to be coded in a way that utilizes all cores available in a processor...
