Computers in commercial use are useless without an operating system. Also, besides an operating system, a computer has a few parts which together make one unit called a computer system. An operating system connects all those parts together and allows for easy access to the computer, and allows communication between the user and the computer through the graphical interface. The first operating systems were developed during the 1950s, and the development of operating systems that we know today began in the 1980s and continues to this day the most popular ones are Windows, Linux and Mac OS. Today's computers are based on the concept model described by John Von Neumann in 1945. like the '45 model, a modern computer consists of input units and output units, an arithmetically-logical unit and a control unit. Controlling the memory is a function of the operating system that controls the primary memory and transfers processes back and forth between the main memory and the disk between execution. Controlling the memory tracks every memory location, regardless of it being used by a process or not. Controlling the memory determines which process will use the memory and at what time. It also tracks the memory to check whether it is used or not and accordingly update its status. Two memory types exist: Random Access Memory (RAM) and permanent memory. The goal of the paper is to explain how an operating system works inside a computer and give a detailed explanation of controlling the memory inside the operating system. The basic principles of the initial computer model from 1945 are described in detail to set ground for more detailed analysis of problems with controlling the memory. The most important chapters are: controlling the memory, file subsystem, and multi-disk redundant containers.