The main difficulty a programmer must overcome in writing an operating system for a real-time environment is that the efficiency of the system must be extremely high and it must have strict time constraints.

Let's begin with a couple definitions and a distinction. A computer operating system allows users to access and operate programs and applications on a computer in an efficient manner. It manages the computer's processes and memory and allocates various resources to programs and tasks. Regular operating systems like Windows or Safari try to do this as close to real time as possible, but there are no guarantees that tasks will be completed at any given point. We've all experienced delays on our computers and have had to wait for one task to finish before we can start another.

A real-time operating system attempts to do everything a regular operating system does only with a faster response to commands so that it seems like everything we ask the computer to do is being done in "real time," as soon as we ask. It looks like the system is doing multiple tasks at the same time, but it really isn't. Rather, a real-time operating system switches speedily between tasks and programs.

We can see the difficulty for programmers as they develop a real-time operating system. They have to figure out a way to make the system switch between tasks and programs so quickly that it seems to be doing more than one thing at a time. This requires strict time constraints, and if these aren't met, the whole system could crash. The level of efficiency must be extremely high, and the programmer must come up with a scheduling strategy that allows the system to switch quickly enough to meet the time constraints.