Higher Systems Computer Software

Operating System (O/S) ► The O/S controls the computer. It controls communication with peripheral devices. It loads programs into memory. It decided where to save files on the hard disk. It allows users to give commands to the computer. ► Without an O/S, a computer is simply a collection of expensive electronics.

O/S

Bootstrap Loader ► Booting a computer means to start it up! ► The bootstrap loader is a small part of the O/S saved in ROM. ► It is responsible for loading the rest of the O/S every time the computer is started (booted) or re- booted.

O/S – Functions ► There are five main functions the operating system performs; ► Command Language Interpreter (CLI) ► File Manager ► Memory Manager ► Input/Output ► Kernel (Process Management)

O/S - CLI This is the type of Interface the O/S provides. It takes commands from the user, checks them and then passes them to the correct part of the O/S to be carried out. We use Menu, Graphical User Interfaces (GUI) and Natural Language (voice Recognition). User actions such as mouse clicks to open files are the type of commands a GUI interprets and passes on to the lower layers of the O/S.

O/S – File Management This organises files on Backing Storage. It maintains a directory which keeps track of where files are physically stored on a disk. This information is needed by the I/O system to find and load files when instructed to do so by the File Management System (FMS) It uses a Hierarchical system storing files in separate directories & sub directories.

O/S – Memory Management ► This controls where data and programs are placed in the millions of memory storage location. ► It keeps track of the amount of memory available. ► If there is insufficient memory to load a program, it sends an error message to the CLI. ► Where more than one in memory is multi programming. O/S Word Halo

O/S – Input/Output ► Also known as the BIOS. ► Performs the actual transfer of data between peripherals and the processor. ► Buffers data to compensate for speed differences. ► Stored in ‘Flash ROM’ for ease of updating.

O/S - Kernel ► Ensures that the processor is always kept busy. Maintains a queue of processes ready for the processor. ► This is done by the scheduler which decides which process should be taken from the queue to be executed!

O/S - Kernal readyrunning readyrunning Blocked Blocked

O/S – Working in concert Load myfile.doc from backing store 1. Issue command to the CLI. 2. Kernel suspends current process & passes request to FMS 3. FMS requests I/O to read disk directory & display filenames. 4. CLI allows user to choose the file from a menu list. 5. FMS passes physical location of file to the I/O 6. I/O loads the file from disk & hands over to the MMS 7. MMS places the file in memory.

Utility – Virus Checker ► A virus is a program that causes damage to a computer, perhaps by deleting data or displaying foolish messages. ► They can copy themselves through infected disks or . ► Virus checkers detect and remove these programs. ► New viruses are constantly being written so this software needs to be run and updated frequently.

Utility – Disk editor (disk clean up) ► This lets you get rid of unnecessary files that clutter up your system. ► It help free up disk space. ► Also comes with a disk repair program as users make frequent mistakes!

Utility - defragmenter ► Over time parts of files and programs become scattered over the surface of the disk. ► It reunites scattered file fragments. ► Read/write heads then have less to travel and files load quicker.

Utilities Other common utility programs ► Backup ► Converters ► Compressors/Expanders ► Installers/Uninstallers ► Printer Drivers ► /Web Filters