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1 Fundamental hardware and software concepts - Coggle Diagram

- - - - An operating system (OS) is the software responsible for the control and management of hardware and system operations such as data input and output, as well as for running software. Common operating systems for personal computers include Linux, Mac OS (for the Apple Mac) and Windows.
        The operating system acts as an intermediary between the user, applications and the hardware, as shown in Figure 1. It enables the user to carry out a variety of tasks on the computer, without the need to know anything about what goes on ‘inside the box’.
        
        The operating system is responsible for:
        
        management of memory
        
        control of peripheral devices (e.g. mouse, keyboard, disk drive)
        
        scheduling access to the CPU, so multiple programs can be run concurrently
        
        providing an application programming interface (API), so programs can access features of the platform simply (e.g. an API makes it easier for a program to have a print feature in its menu)
        
        providing a user interface, such as Windows, or Gnome on Linux.
        
        Starting the computer involves a small 'bootstrap' program accessing read-only memory (ROM) and loading the operating system.
      - 1.3 How programs run on a computer
        
        When writing software, we prefer to use a language resembling a natural language that can be understood by human beings. The source code we produce in a particular programming language must then be translated into a primitive language called machine code – the instructions that can be understood and run, or executed, by the hardware of a computer. We call the programming language a high-level language, while machine code is a low-level language.
        
        Translation of the high-level language source code to a low-level machine code program is usually carried out by a piece of software called a compiler. Translation can also be done by an interpreter, which translates a line of source code (as opposed to a whole program) into machine code, as and when it is required.
        
        During compilation a compiler must first check that the source code conforms to the syntax rules of the language; that is, whether it is properly formed. Only if this check is successful does the compiler produce the machine code that will be executed.
        
        The major problem with this simple model of compilation is that the compiled code is not portable, as different computer types employ different machine code languages. If you wish to move software from a PC to a Mac, you would have to recompile the high-level language source code with a Mac-specific compiler to produce Mac machine code (see Figure 3).
        
        Another, more portable, model of compilation makes use of a special layer of software called a virtual machine (VM) that resides ‘on top of’ an operating system. A virtual machine mimics the behaviour of a computer and has its own instruction set, just like a real CPU. In this model of compilation, the high-level language source code is not compiled to a hardware-dependent machine code. Instead, it is compiled to an intermediate code, which is the machine code of the virtual machine. In Java environments, the virtual machine code is called bytecode because each instruction is a byte in size. Using this intermediate code approach allows low-level, essentially executable, code to be moved unchanged between different computer systems (see Figure 4).
        
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