A computer that is running has two main parts. It is hardware and software. Hardware refers to the machine itself of a computer. Software refers to a program running on hardware. It is the same as the relationship between the game machine itself (= hardware) and game software (= software).
There are two main types of software. It is basic software and application software. Basic software is called Operating System (OS). Application software runs on basic software.

1.1.1 OS role

If we say extremely, the basic software "do nothing by itself. " It provides very basic functions only. For example, in the windowing application software you are using, there are menus, dialogs are displayed for warnings, and there are buttons for confirmation. If these are prepared by each application software, it will be very difficult to create application software. One of the major roles of basic software is to provide functions commonly used by application software.
Besides that, there is a function of "managing resources". "Resource" in this case indicates the function and capability that the computer can provide. For example, you can run word processing and spreadsheet software at the same time. Originally, computers can only process one process at a time. Despite that, we can use them at the same time, because each software is switched at very short time. This is the function controlled by the OS and it can be said that it manages "resources" called hardware.

1.1.2 Convenient points and inconvenient points in OS

OS provides a variety of functions, it absorbs hardware differences and is very useful. However, since the OS itself consumes the "resources" of the hardware, it is not always valid in all cases.
For example, it is a vending machine located in the city, but the function is limited to some extent, so there is no function equivalent to the OS. Since it is inevitable that the OS itself can cause trouble, it is designed as simple as possible.
Also, the mobile phone of a long ago had no OS. However, recent mobile phones have become extremely versatile, such as access to e-mails, mobile websites, mobile applications, etc. besides calling. As a result, it is judged that the introduction of OS is appropriate, and most of the mobile phones in recent days have OS introduced.