The OS - Systems Software

• Systems software is software designed to run and maintain a computer system. By far the most important one is the operating system (OS)
• Operating systems manage hardware and run software
• An operating system (OS) is a complex piece of software found on most computer systems
• Functions of an OS:

  -Communicate with internal and external hardware via the device drivers

  -Provide a user interface, allowing a user to interact with the computer and vice versa

  -Provide a platform for different applications to run
• Functions of an OS:

  -Allow the computer to multi-task by controlling memory resources and the CPU

  -Deal with file management and disk management

  -Manage system security and user accounts
• The words 'application' and 'program' can be used interchangeably to describe computer software
• Device drivers let the OS and hardware talk to each other
• OSs use a device driver software to communicate with internal hardware or peripherals connected to the computer system
• Every piece of hardware connected to the computer system requires a device driver. Drivers essentially act as a 'translator' for the signals between OS and hardware
• When a computer is booted up, the OS will choose the correct device drivers for the hardware it detects
• If new hardware is connected to the computer, the system will install the new, matching driver
• Device manufacturers may release updates to device drivers in order to fix bugs, add features or improve the performance of their hardware
• Updates may be installed automatically by the OS or manually by the user
• Operating systems provide a user interface
• A user interface allows the user to interact with a computer system
• Graphical user interfaces (GUIs) are the most common type - they're designed to be easy for everyday users by making them visual, interactive and intuitive
• GUI systems are optimised for specific input methods. In the past, GUIs have been WIMP-based (using windows, icons, menus and pointers).
• Android and iOS were created for touchscreen devices, using finger gestures like pinching and swiping in place of a mouse
• A command-line interface is text-based. The user enters specific commands to complete tasks
• Command-line interfaces are less resource-heavy than GUIs
• Command-line interfaces aren't suitable for everyday users. But for advanced users, they can be far more efficient and powerful than a GUI.
• Command-line interfaces can be used to automate processes using scripts (simple programs)
• The OS allows multi-tasking by managing resources
• OSs provide a platfrom to run applications (by configuring hardware so they can use it, and giving access to the CPU and memory)
• Operating systems can run multiple applications at the same time are called multi-tasking OSs
• The OS helps the CPU carry out multi-tasking by efficiently managing memory and CPU processing time
• When an application is opened, the OS moves the necessary parts of the appliation to memory, followed by additional parts when they're required. The OS will decide is applications or features have been used recently - if not, they may be removed from memory
• To run multiple applications, the OS needs to make sure that the applications don't overwrite or interfere with each other
• A memory manager allocates certain applications certain memory addresses, to make sure their processes are placed into separate locations
• Only one application is processsed by the CPU at a time, si the other processes must wait - fortunately the CPU can switch between applications extremely quickly -
• The OS divides CPU time between open applications and may prioritise certain processes in order for instructions to be executed in the most efficient order
• When required, the OS organises the movement of data to and from virtual memory
• The OS also helps manage the flow of data in the system bu using memory buffers
• Different types of computer components, devices and processes will send, receive and process data at different speeds - temporary memory buffers store data until the component, device or process is ready
• The OS handles file and disk management
• Computers store data as files. Images, music, videos and spreadsheets are all just collections of data
• File extensions tell the computer which type of file it is (e.g. .jpg)
• The OS is responsible for file management - the organisation of data into a usable hierarchical structrure. It also deals with the naming, saving, movement, editing and deletion of data
• The OS manages the hard disk. It splits the physical disk into storage sectors, decides which sectors to write data to, and keeps track of free space on the disk
• Ideally, the data for a single file would be placed in adjacent sectors, but this isn't always possible