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Display space is similarly shared; the operating system will ensure that multiple programs can each display in their own windows, but prevent them from destroying graphics being displayed by other windows.
=== Security Enforcement ===
It’s important to keep information private in some contexts, and to share information in other contexts. The operating system is responsible for enforcing security rules. For example, on a smartphone, a social media app shouldn’t be able to access data from a banking app, and on a cloud server, one customer shouldn’t be able to access another customer’s data. However, multiple smartphone apps might be permitted to access a photo album, and a company employee might need to view a report generated on a server from multiple customers’ data.
The operating system is responsible for enforcing the security policy.
=== Hardware Abstraction ===
There are many different types of devices that perform similar functions, and multiple ways that these devices can be connected. For example:
* A keyboard may be connected via a USB connection, or a wireless Bluetooth connection.
* A mouse may be connected via a wired USB, wireless USB, or wireless Bluetooth connection. But there are also other types of devices which can provide the same capability of allowing the user to interact with the display, including trackpads, trackballs, and touchscreens.
* Sound may be played over built-in speakers, an external analog speaker, an analog headset, a digital speaker or headset with a USB connection, a Bluetooth speaker, earbuds, or headset, or played through a television connected via HDMI.
The operating system also abstracts hardware details. This means that programs can access devices in a general way without having to be programmed to individually deal with each type of device that may be used. This enables a program to request keyboard input or play sounds without regard to the details of the specific hardware available.
=== Maintaining the Programming Model ===
The operating system, computer hardware, and development tools (compiler, linker, and so forth) work together to present the “programming model” – a conceptual framework which software developers use when creating software. For example, several different application program may be designed to occupy the same area of memory; obviously, this presents a conflict when these applications are used at the same time, so the operating system works with the computer’s hardware to load the applications into different areas of physical memory, and then use the computer’s virtual memory capabilities to make each program appear to be loaded into the region of memory for which it was written.
