The chief program that manages all of the hardware and software, it has control of every process, file, section of memory and device. It is basically a middle man ensuring that both the hardware and the software work correctly.

Checks every type of file that is on the system including data files, program files, compilers and installed applications. It sets permission so that certain users can only see certain files. 

Decides how to allocate the brain of the computer, known as the Central Processing Unit (CPU). It keeps track of the status of each process. It handles jobs as they enter the system and manage each process that are associated with them.

Is in charge of the main memory. It scans every request for memory space and checks if it is valid. It allows allocation of free memory spaces and deallocation of needed memory spaces.

Manages every device, channel and control unit. It chooses the most efficient way to allocate all the devices connected to the computer (USB sticks, printers, external drives ... ).