The biggest part of systems software is the operating system. it is an essential part that allows other systems software, and application software, to communicate with hardware. The operating system is needed to perform a number of tasks. It provides a user interface, manages the use of memory and the opening, closing, saving and deleting of files. Most operating systems have features that look after the security of the computer with usernames and passwords. Applications software is used to carry out tasks on a computer, such as writing an email, making a poster, doing homework and messaging friends.