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Software
what we cannot touch (programs and data)
Programs: operating system and application programs
Operating system – is loaded into the operating memory after we switch on the computer. It makes all the other parts of computer to start working and controls them. It also provides the interface (rozhraní, mezičlánek) to the user and to the application programs.
Applications (application programs) are computer software designed to help the user perform a certain task. Such programs are sometimes called software applications, or application software. Typical examples are word processors, spreadsheets, media players and database applications etc.
 
Operating System
An operating system (OS) is an interface between hardware and user which is responsible for the management and coordination of activities and the sharing of the resources of the computer that acts as a host for computing applications run on the machine. It relieves application programs from having to manage these details and makes it easier to write applications.
The operating system is the most important software component of your computer. It performs many functions and is, in very basic terms, an interface between your computer and the outside world.
Operating systems provide communication with all hardware parts of the computer. The same operating system can run on computers with different hardware (but there are limits). Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers and manage (řídí, zajišťuje chod) processor and operating memory.
Operating systems provide a software platform on top of which other programs, called application programs, can run.
As a user, you normally interact with the operating system through a set of commands. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen.
Functions
·         Manages and communicates with all hardware parts of the computer (RAM, processor, HD)
·         Executes applications and provides a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware. (write)

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-      Communicates with users

·         Manages files in memory storages

 

 
Operating systems:
DOS, Windows, Unix, Linux, Mac OS ..
How it all works:
Tracing the Flow of a Keystroke
• When               a key is pressed, the keyboard generates a code. The keyboard controller interprets the code and raises its hand, that is, sets an interrupt. An interrupt controller takes note of the interrupt and where it came from, then alerts the CPU.
•The CPU calls on the keyboard controller, which points the CPU to the buffer, a small, special purpose memory location, where the code is stored.
•The CPU passes the code on to the operating system for further processing.
•The operating system passes on the code to the active application for final processing.
•The active application chooses to either ignore the keystroke if it is not programmed to attend to that particular keystroke, or take a specific action as defined in its programming code.
 
Displaying a Character on a Monitor
•The active application sends the display request to the CPU.
•The operating system raises its hand (generates a software interrupt)
•The CPU pauses what it's doing to retrieve the request from the operating system
•The CPU sends the instructions for the display to the video controller
•The video controller sets an interrupt and then sends the information to the graphics processing unit
•The GPU calculates which points on the monitor should be shaded in which way to create the new display.
•The GPU writes the information to video memory and also sends it to the display
•The display redraws the screen using the new information.
 
Application programs
A program or group of programs designed for end users. Applications software (also called end-user programs) includes database programs, word processors, and spreadsheets, web browsing, desktop publishing, accounting, games, graphics and design applications, communications etc. Figuratively speaking, applications software sits on top of systems software because it is unable to run without the operating system. Operating system enables programmers to write application programs which can run on computers with different hardware parameters.