Outcome 2 – Computer Software The Range of Software Available • The Different Categories of Software • System Software • Programming Languages • Applications Software 2 – System Software 2.1 -The Operating System • Manages the hardware & communicates with the user. • O/S is broken down into layers so updates can be written for specific layers. • Some parts of O/S held in ROM chips, but most parts held on disk – can be corrupted. • Bootstrap program runs on start-up and loads in the rest of the O/S from disk. Operating System Layers I/O Kernal 2 – System Software 2.1.1 –Single-user Operating System • The tasks of a single-user operating system is to manage all the resources of a computer system. • The main resources are. – File management. Memory management. Command language interpreter. Input - Output System Process Management 2 – System Software Single-user Operating System -Command Language Interpreter • The operating system takes user commands from the keyboard and mouse. • Passes them to the operating system which; – Carries out the command. – If command cannot be understood an error is reported and a suitable message given back to the user. 2 – System Software Single-user Operating System -File management • The operating system supervises the creation, deletion and updating of files on backing storage • A directory keeps track of where files are stored. This is a hierarchical directory structure in which files are placed in folders (directories) and sub-directories 2 – System Software Single-user Operating System -Memory management • The operating system decides where programs and data are to be placed in main memory • It also keeps track of what stage a program is at and this applies equally to the operating system's own memory space. • If corrupted it could cause the computer to crash 2 – System Software Single-user Operating System - Input-Output System • Peripherals all work at different speeds • The I/O system hides the differences and it makes them all appear to operate in a similar manner. • The I/O system does all the actual data transfers and issues the appropriate control signals to the peripherals. • Manufacturer usually supplies software (called a driver) for the user to install on their hard disk. 2 – System Software Single-user Operating System - Process Management • O/S decides which tasks get to use the processor • Processor management is often called the Kernel of the system • It is the core function of the OS 11 File management 2 – System Software 2.1.2 Network Operating System • All Stations should have the same O/S to use the network system and to share messages on the network system. • Multi-User Access – Operating System must provide a “logging-on” procedure with passwords for security.The user ID controls what the user has access to on the network. • File Attributes – A user usually has read/write (r/w) access to their own files, read-only access to shared files. 2 – System Software 2.1.2 Network Operating System • File and Print Services – different users have different levels of access. • Data Sharing and Integrity –. Only one user can edit a shared file at any one time (locking-out system). 2 – System Software 2.2 Utility Programs • Utility programs aid the maintenance of the computer or make the user’s life easier. • Includes disk formatter, disk tools and defragmentation tools. – Files are saved wherever the system can find space in consecutive sectors. As files are added and deleted spaces become available and are all over the filing system. A de-fragger moves files around to create a contiguous system with no empty sectors. 2 – System Software 2.3 Translators • A Translator turns a program written in a highlevel language into machine code. • The high-level language is the source code and the machine code is the object code. • Compilers – translate the source code in one go and produces executable machine code. • Interpreters – Translate and execute a program line by line. Interpreted programs run much slower than compiled. Interpreter is simpler to learn and use. 4 – Application Software 4.1 Types of Applications • You need to be aware of applications which handle:– – – – – – – Text (word processor, web browser) Number (spreadsheet, accounts package) Data (database, world wide web) Communications (e-mail, file transfer) Graphics (painting, drawing, CAD) Multimedia (sound, video) Integrated Packages (Works v Office) 4 – Application Software 4.2 Features and Requirements • All application packages have features which distinguish them e.g. – Database – search and sort data, print reports. – Multimedia – allows user to create presentations using sound and video. • Application packages have minimum hardware requirements. – Memory – Minimum RAM used is specified. – Hard Disk – Minimum disk space for installation and running usually specified. – Processor and operating system. – Any specific peripherals. 4 – Application Software 4.3 Standards • Each application package saves files in its own way. Standards set ways of saving data so other packages can read the data. – – – – SYLK, standard for spreadsheets RTF, standard for text CSV, comma separated variable for database JPEG, GIF, TIFF, for graphics