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					Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation

Hamilton Grammar School ICT Department

Computer Software
Learning Criteria & Self Evaluation 2008 - 2009 Higher Computer Systems Student Name: __________________________
Complete the smiley or colour it in - for each bit of information in this book (but only for the pages you are told to read)

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I know exactly what this means and can explain it

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I know what this means but I find it hard to explain

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I don’t know at all what this means Help Me Please!

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Unit 5 – Computer Software Operating Systems The OS is a program which controls the operation of the computer and any of the devices attached to it. The OS is running from the moment the computer is switched on until the moment it is turned off. ROM based operating systems are ones which are stored on ROM chips. To update the OS would require removing and replacing the ROM chips Disk based OS are easy to update, new features can easily be added as well as new hardware. Another advantage of a disk based OS is that some parts of the OS can just be loaded as and when required.

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation The Bootstrap Loader The Bootstrap loader is a small part of an OS which is saved in ROM. Its function is to load the rest of the OS from disk when a computer is switched on. The Disk Based OS can take up a substantial part of the Computers main memory once it has been loaded. Because the OS is based on disk it is possible to corrupt it. This may be due to malicious code (viruses) or bugs in the code. The Single User Operating System Single user simply means that it is only capable of supporting one user at a time A Network OS is designed to support multi-access operation. The functions of a SUOS  Interpreting user commands  File Management  Memory Management  Input/Output Management  Managing processes  Resource Allocation Page 3

Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation The structure of the OS The outer layer being closest to the user. (The Onion bag Diagram)
CLI FMS MMS I/O

Kernel

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Interpreting Users Commands Command Line Interpreter

This is the outer layer through which the user interacts to give instructions to the computer. It may be command driven which means the user will enter typed commands to it. It may be menu driven which means the user will choose commands from a list (this means it will use a GUI) Its job is to interpret “make sense of” the commands entered by the user and get them carried out. If anything goes wrong the CLI would respond with an error message. These usually make use of context based help systems which provide help based on the activity the user was doing when the error occurred. For example, a printer help message if the problem occurred whilst trying to print. This will also include when users try to delete important data from a system. The CLI is a process which runs on a Computer System. When you give the CLI a command the CLI simply copies the command to the next layer of the OS. When this happens the CLI is blocked and will not accept any more commands until the process is complete Page 5

Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation File Management – File Management System FMS The FMS is concerned with the efficient use of the computers backing storage devices and media. It is also known as the DOS (Disk Operating System) As well as storing the files on the disk the FMS also uses storage space to hold the details of where the actual files are saved. This is held in the disk catalogue (usually held on the outer tracks of the disk surface) The catalogue also holds the details of the precise physical address on the disk where the file can be found. The precise physical address is required by the Input/Output management system in order to find and load a file when instructed to do so by the FMS. The files are organised in a hierarchical filing system using separate directories and sub-directories.

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Memory Management – Memory Management System (MMS) This layer controls where programs and data are stored in memory. It keeps track of the total memory available, which programs and data are currently loaded The MMS allocates space in memory for programs and data. Sometimes if there is not enough memory to open a program then the MMS will send a message to the CLI to inform the user. MMS are capable of multi-tasking which will allow more than one program loaded into memory at the same time. It also ensures that none of the programs interfere with the area of main memory which is used by the OS. If this was to happen it would cause a System crash which would mean the loss of any unsaved memory.

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Input/Output Management – I/O Systems This layer is also known as the BIOS or Basic Input Output System. The computer hardware manufacture will provide the BIOS as it needs to be tailored to suit the particular hardware. The I/O system communicates directly with the peripherals and handles the transfer between the peripherals and the processor. Some BIOS are stored in Flash ROM to allow them to be easily updated. Process Management – the Kernel The kernel (not to be confused with the Colonel) is the part of the OS responsible for managing processes and handling any interrupts. Interrupts (remember?) are signals used by the peripherals to communicate with the processor. Blocking the CLI is an example of how the OS manages a process Page 8

Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Resource Allocation Any process (such as a user program) requires resources. The resources it will require are such like  An area of the Computers Memory  Access to data in a device interface buffer  One or more files  Some part of the processors time Resource Allocation is the management of the resources available at any one time. Efficient management ensures that the processor is constantly kept busy by keeping a queue of processes that are always ready for the processor. The scheduler makes the decisions on which process is given the processors time. A process may be in several different states  Running – currently has the processors time  Ready/Free – could run if given the processors time  Blocked – a process which cannot run as it is waiting for a resource which is allocated to another process  Terminated – a process which has finished Page 9

Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation A computer with only one processor can only run one process at a time. It may appear that the processor is running two or more processes; really the processor is just dividing its time between each process using time slicing. Processes can also be given a priority (High -> Low) High Priority can be given more time slices. Multiple Processor computers can run multiple processors simultaneously. Programs which are capable of simultaneously processing are specially written to do this. This means that processes which are run simultaneously must be independent of one another so that no blocking can take place.

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Software Compatibility Issues This is where software which runs on a particular system is said to be compatible. There are some issues which affect whether software will run on a particular system. Memory Requirements As programs become more and more complex the demands on RAM memory also increase. The technical guide for a program will specify the amount of RAM memory (free and unused) is required to run. Storage Requirements This refers to the amount of free backing storage space required to install the program. To counter the problem of not installing properly options are given for a Complete, Custom or minimal installation to save of storage space. OS Compatibility Software which is compatible with one OS is suitable for that OS and no other. Even with earlier versions of OS (windows 98, Windows XP, Windows Vista) some software will not be compatible on the older versions of the OS.

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Working Together Loading a File from backing storage involves all layers working together like so (in a simplified manner) Trying to open a file 1. CLI is given the command OPEN by the user selecting a menu or entering a Command 2. Kernel suspends current CLI process, the request is then passed to the FMS 3. The FMS requests the I/O system to read the catalogue track and load a list of file names 4. The CLI lets the user select a file from a list 5. The FMS passes the physical location to the I/O system 6. I/O system loads the file from disk and hands it over to the MMS 7. MMS places file in memory 8. Kernel allows the CLI process to resume, control is given back to the user

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Utility Programs A utility program is system software designed to perform an everyday task. (Transferring data from one backing storage device to another or editing the contents of a disk directly using a disk editor) Virus Checker Very much an essential utility, this software should be able to detect and remove a virus from a Computer System. This will involve checking of files downloaded from the internet to ensure they do not contain a virus. As new viruses are being constantly written virus software companies allow updates to be downloaded to ensure that the virus checking utility program is always up to date.

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Disc Editor This allows the user to edit data directly on the surface of a disk. This carries the risk of completely destroying all data if you don’t have a Scooby! Most of these come with Disk Repair functions to recover and repair damaged data. These usually repair errors mostly in the disk catalogue which prevent you accessing your files. Most disc editor programs save a copy of the disk catalogue – speeding up recovery. Disk journaling – writes changes to a special area set called a journal. Reduces chance of data being lost because FMS can restore, using disk journaling to the last known good state. This means data takes longer to be written to disk Smart Disk – monitoring and self analysis feature which report the condition of the hard disk and gives notice if it is likely to fail

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Disk Defragmenter Filing systems try to save files on adjacent blocks in memory. But over time as files are deleted it is not always possible. This means some files are split up over a surface area on a disk meaning it takes more time to load. A defragmenter arranges all the blocks of data so that all free spaces are grouped together and conjoins all the file fragments which have become separated. This improves the performance is that it reduces the distance the read-write head has to move to find all the blocks in a file.

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Backup Backup software automates the process of backing up software. Backup allows you to select the type of backup media, the frequency of the backup and the time for it to take place. Emulators This allows one computer to act is if it were a completely different computer. This allows software to be used on a computer other than the type it was designed for. Converters These convert the file types from one application package into another type which can be opened by a different application Compressors/Expanders These allow the user to reduce the file size – for example graphics compression techniques Installers/Uninstallers This is used to put an application program on the computers hard disk Page 16

Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Printer Drivers This takes the codes used in a document (for BOLD, Underline, Italic etc) and translates them into the correct code for the printer in use Email and Web Filters An Email filter simply filters out emails containing unsuitable language or which come from certain addresses Web Filters provide the same function on URLs Standard File Formats These allow users to transfer data between different packages. For instance word processing documents from Microsoft Word to Apple Works (and anyone who has Windows Vista who tries to open a .docx file in school!) Standard Graphics File Formats GIF – Graphics Interchange Format JPEG – Joint Photographic Experts Group TIFF – Tagged Image File Format Page 17

Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Selecting Software for Tasks You should know the names of which software (and why) they can be used to produce certain Production of a multimedia catalogue HyperStudio or Macromedia Director Setting up a LAN in a school Microsoft Windows Server or MAC OS X Development of a school website Microsoft Frontpage or Dreamweaver

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Virus, Worm or Trojan Horse A virus is a program which will destroy or cause damage to a computer system. This includes worms and Trojan Horses A worm is capable of making copies of its self. It then spreads itself to other systems without having to be attached to a file. A virus infects other host files and is distributed along with them. A Trojan horse is usually disguised as another time of file – in some cases posing as an anti-virus utility program. These are all grouped together and called malicious software or malware. This also includes spyware, browser hijackers and re-diallers. Virus These must be run in order to infect a Computer System. They can attach themselves to other programs which ensure that this happens. This can result in various different effects

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Viruses are capable of  Corrupting or deleting data from a storage

medium  Restarting your computer system without warning  Disable the computer by changing the OS  Cause silly messages to be displayed or producing unwanted sounds  Generate so many email messages that they cause email servers to crash  Record every key that is pressed and send all these (which would include passwords) to the virus writers computer  Use your computer to attack other computers by generating spam or overloading a company website with data (which you can be held liable for) You can catch a virus from, infected floppy disks/CDs, downloading from websites, opening files received via email.

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation

Worm
These function differently to viruses. They can spread themselves to other computers without needing to be part of a “host” program. An indicator that a worm has infected your system would be the memory unexpectedly filling up. Worms generally come through email, but they can also infect systems by Trojan Horses containing worms! Trojans This refers to a program that appears to be safe but usually contained within is something harmful An example would be downloading something, but when you run the file the worm or virus contained within gets to work. Some Trojans, known as backdoor Trojans, allow the person who sent it to you can take control of your computer over the internet. (For example sending spam messages)

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Classification of Viruses Viruses are classified by the types of file which they infect. File Virus These attach themselves to files, inserting malicious code into files. Boot Sector Virus All disk drives contain boot sectors. It contains information about the format of the disk and a small program called the boot code. When a virus infects this code it can guarantee to be run. Macro Viruses Certain programs allow users to create and embed macros in a document to automate a sequence of operations. This type of virus can cause a malicious series of actions to be performed when the document is opened. It can destroy data or place up strange messages.

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Virus Actions Replication Worms can make copies of themselves – this is known as replication Camouflage Viruses try to hide their existence. One method they use is to mix fake programming code with their malicious code in the hope of not being recognised by an anti-virus program Watching This type of virus waits until a particular date or until a particular action before it is executed. Watching for action – Logic Bomb, for date – time bomb. Delivery This is the method in which the virus enters the system and cause the infection. Infected floppy disks used to be the most common method of infection. Nowadays security flaws in the OS allow viruses to infect systems. Email is another method as well as file sharing and instant messaging. Page 23

Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Anti-Virus Software Detection Techniques Use of Checksum A checksum is calculated using a given set of data. It is transferred along with the data to ensure it has been sent and received properly. The transmitting system calculates the checksum and transmits it; the receiving system repeats the calculation and compares the checksums. If they do not match it knows an error has occurred. For Viruses, a checksum is calculated on an uninfected program. Repeating the process on a suspected infected program allows the Anti-Virus software to see if the program has been changed. If so it will issue a warning. Searching for Virus Signature This involves scanning for pieces of code which is a characteristic pattern of bytes which is a virus. This is why it is important to update your anti-virus software as it updates its record of Virus Signatures.

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Hamilton Grammar School
ICT Department Higher Computing

Learning Criteria & Self Evaluation Heuristic Detection Heuristic Detection follows a simple rule of thumb. These allow rules to be set up to detect new viruses which have not been seen before. An example heuristic – if it looks like a virus, if it behaves like a virus then it probably is a virus. Memory Resident Monitoring This software loads into the computer when it is powered on staying there until shut down. It does this in order to monitor the computer for the presence of viruses. This may slow down the operation of the system. Hoaxes This is simply a report of a nonexistent virus. In general emails are sent out describing some form of virus and describing what to do to get rid of it, telling you to forward it to your friends. The resultant flood of emails can cause mail servers to crash

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