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Higher Computing Computer Systems. Computer Software. What is an operating system. The operating system is a program that controls the entire operation of the computer and devices which are attached to it
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Higher Computing Computer Systems ComputerSoftware
What is an operating system • The operating system is a program that controls the entire operation of the computer and devices which are attached to it • Most of the OS is permanently stored on hard disk and loaded in to RAM when the computer is on
The bootstrap loader • When the computer is switched on the initial part of the OS is loaded from chip (ROM) • The bootstrap loader’s function is to load the rest of the OS from disk
The single user operating system • A SUOS is only capable of being used by one person at a time • The main functions of a SUOS are: • Interpreting users commands (CLI) • File management • Memory management • I/O management • Managing processes • Resource allocation
The Command Language Interpreter • The CLI is the layer with which the user interacts in order to give instructions to the computer – it interprets user commands
File management • The FMS is concerned with the efficient use of the computer’s backing storage devices and media • The FMS holds the details of where each file (or part of) is held on the disk • The FMS is also known as the Disk Operating System
Memory management • The MMS controls where programs and data are placed in main memory • The MMS keeps track of the total amount of main memory available and which programs and data are currently loaded
Input/Output management • The I/OMS communicates directly with the peripheral devices • The I/OMS handles the transfer of data between the peripherals and the processor
Process management – the kernel • The kernel is the part of the OS which is responsible for managing interrupts • e.g. from the printer • The kernel is responsible for managing processes • from the CLI e.g. copy. A process initiated by the CLI may result in an interrupt
Resource allocation • RS is the way of managing which resource is available for use at any one time by a process • Efficient RS ensures that the processor is kept busy, by maintaining a queue of processes that are always ready for the processor • A “scheduler” prioritises the queue
The OS working - an example • Loading the file “myfile” from disk • Using the CLI you issue the command to open a folder • The kernel interrupts the current CLI process and passes the request to the FMS • The FMS requests the I/O system to read the disk’s catalog track and loads a list of file names • The CLI allows the user to choose the filename “myfile” from the list • The FMS passes the physical location of the file to the I/O system • The I/O system loads the file from disk and hands it over to the MMS • The MMS places the file in the main memory and you again have control of the computer
Utility programs • UP’s can be part of the OS or a separate program • Virus checker • Disc editor • Defragmenter • Backup • Emulators • Converters, compressors and expanders • Email and web filters
Virus checker • A virus checker is a utility program which is designed to check a computer system for viruses • A virus checker will then remove the virus • Virus checkers have to be kept up to date in order to be effective against new viruses
Disc editor • A disc editor allows the user to edit data directly on the surface of a disk • DE programs incorporate automatic disk repair and data recovery functions • Newer hard drives “smart drives” have their own software for which monitors the performance of the drive
Defragmenter • Files are often split and saved on different parts of a disk • This increases the time taken to access the file • A defragmenter gathers all the free space on the disk together and reunites all the fragmented files that can be accommodated
Before defragmenting After defragmenting Used block unused block
Backup • Backup software can help to automate the process of making regular backups • Backup software can allow you to synchronise files between two devices or media • When two copies of the same file exist on different media the newer copy will replace the older version
Emulators • An emulator is a program that allows one type of computer to behave as if it was a completely different type • A computer running emulator software will run much slower than the computer it is emulating • Virtual PC allows apple computers to emulate Windows OS computers
Converters, compressors and expanders • Converters change the format of a data file from one application type to another • Compressors reduce the size of a data file • Expanders decompress a compressed data file
Printer drivers • A program that takes the codes in the document and translates them into the appropriate code for the printer in use
Email and web filters • An email filter is software that monitors emails which are sent on a network • The Regulation of Investigatory Powers Act (2000) gives employers the right to monitor employees email • A web filter monitors URLs and the content of web pages be accessed by the user
File formats • Standard file formats have been developed to ease the transfer of data between software developed by different manufacturers e.g. text files - RTF • Each type of application software has its own set of standard file formats e.g. JPEG used in photographic manipulation software
File formats - GIF • Graphics Interchange Format • For low resolution bit-map colour graphics • 256 colours possible • Compressed files • Fast to load and transfer via internet • Interlacing allowed • Animations also possible • GIF uses lossless compression
File formats – JPEG, MPEG • Joint Photographic Experts Group • Standard for still picture compression • 16.7 million colours • Uses lossy compression • Typically achieves 10 to 1 compression with little perceivable loss in image quality • Motion Pictures Expert Group • Standard for moving pictures
File formats - TIFF • Tag(ged) Image File Format • For high resolution bit-map images • Large files unsuitable for WWW • Uncompressed • Used by DTP, book and magazine printing
Matching software to tasks (1) • Production of a multimedia catalogue • Multimedia authoring package e.g. Macromedia Director • Additional software for editing individual elements • Video • Audio • Graphic • Text • And • CD or DVD writing software
Matching software to tasks (2) • Setting up a LAN in a school • Modern OS capable of peer to peer networking • Client server needs network OS software • Database servers need specific software e.g. Microsoft SQL • Database application such as Filemaker Pro are available in single or network versions
Matching software to tasks (3) • Development of a school website • Web page creation software with WYSIWYG page editing • Additional software for editing individual elements • Video • Audio • Graphic • Text • And • Testing using a range of browser software
Software compatibility issues • Software that works on a computer system is said to be compatible • Issues that can affect the compatibility of the software are: • Memory requirements • Storage requirements • OS compatibility
Memory requirements (RAM) • If a system cannot meet the minimum RAM requirements to run the software the software will not run • If there is insufficient RAM to hold the complete program then part of it will be stored on disk, virtual memory • Running programs using VM will slow the program
Storage requirements • Full installation - The amount of backing storage needed to hold the complete program after installation (and decompression) • Minimal installation – The least amount of storage requirement needed to run the program, normally the installation CD is still needed to run the program
OS compatibility • Three main OS used on desktops and laptops • Windows • Unix • Apple OS • Users need the correct version of software for the different OS • Windows OS not always backward compatible
Viruses • A virus is a program which can destroy or cause damage to data stored on a computer system • A virus infects host files and is distributed along with them
Worm • A worm is a virus that can make copies of itself and spread between computers without having to be attached to a file
Trojan horses • A Trojan horse is disguised as another type of file
What viruses infect • A virus may infect different parts of the computer system • File viruses • Boot sector viruses • Macro viruses
File viruses • File viruses attach themselves to files • They add malicious code into the files • Typical files that are infected are Windows OS files with .COM and .EXE extensions
Boot sector viruses • All magnetic disks contain a boot sector • The boot code can become infected with a virus and is loaded when the machine is rebooted • Less common now that floppy discs are no longer in popular use
Macro viruses • A macro virus infects documents e.g. spreadsheets or word processing documents • A macro virus causes a malicious series of events once the document is opened • The macro virus will also infect any new documents created by the same application
Virus code actions • Virus act differently according to how they are programmed • The action the virus may carry out when run include: • Replication • Camouflage • Watching • Delivery
Replication • A worm can make copies of itself this is known as replication
Camouflage • Mixed in with good code • Malicious or false code is changed every time it runs to avoid detection • Disguise the code so that it looks harmless • All these techniques are used to avoid detection by anti-virus programs
Watching • Sleeper virus lays in wait for a particular sign which will activate it • A date or time or action • Time bomb (triggered by a date) • Logic bomb (triggered by an action)
Delivery • The method used by the virus to enter the system • Shared backing storage devices • Connected to the internet • Web pages • Downloads • Emails • Email attachments
Anti-virus detection • Anti-virus software detection techniques include: • Use of checksum • Searching for virus signature • Heuristic detection • Memory resident monitoring
Use of checksum (1) • A checksum is a value calculated for a given set of data • The answer to the calculation is the checksum • It is used to check that data has been transmitted and received correctly
Use of checksum (2) • The checksum is transmitted along with the data • The receiving computer performs the same calculation and checks the sum • If they are the same its ok • If the don’t match the anti-virus software will issue a virus warning
Searching for virus signature • Anti-virus programs can find viruses inside programs by scanning them for virus signatures • A virus signature is a characteristic pattern in a file • These files can then be disinfected • Polymorphic viruses modify their code to avoid virus signature detection
Heuristic detection • Detect viruses a heuristic or rule of thumb method • Imprecise method although useful • If it looks like a virus and behaves like a virus then its probably a virus • Used to detect new viruses
Memory resident monitoring • Anti-virus software that loads in to the computers memory on start up • Monitors all programs and data loaded in to the computers memory • Can slow down the processing speed of a computer as everything is checked for viruses