Operating Systems Flashcards
Utility software
File indexing
- An indexed file is a computer file with an index that allows easy random access to any record given its file key.
File conversion
- Convert a sound file from WAV to MP3
Defragmentation
- is the process where files are physically re-arranged on disk so that they are no longer fragmented and the parts of each file are stored together.
Compression
- software reduces file sizes using less space
Task management
- can see how much disk % a given program is using, can shut it down if dominating.
Disk scanning and repair
- fixes problems on disk.
Anti-virus software
- to scan for viruses which could be causing issues with the disk access speed / damaging data
Backup
- software allows users to archive files and delete files on the hard disk to free up space
Firewall
- Prevents unauthorised network access
Human-Computer-Interaction (HCI)
- Common interface devices, including keyboards and mice, are still in widespread use but are starting to be superseded by other human-computer interaction methods.
- Voice input makes use of spoken language to allow interaction with a computer.
- Touch screens are a feature of most new devices and can take advantage of gestures.
- Force feedback offers haptic feedback to the user which is adding a new dimension to human-computer interactions
- Virtual reality uses headsets to immerse the end user in an alternate world where they can interact by moving their bodies. Sensors track a user’s movement and translate it into changes in the world the user is seeing.
- Augmented reality overlays details onto a live camera feed or projects onto glass. It will make use of sensors and other data to give the user a more immersive experience.
- New system design must be validated before being used to ensure that its implementation will match the requirements.
- Prototypes can be used to test out an interface design.
- Feedback in initial stages of a new design can be used to improve it before implementation.
- Evaluation allows the development company and the customer to decide whether a project has been successful. The key issues that need to be part of any evaluation are:
- Ensuring the requirements are met.
- Ensuring the system responds in an acceptable timeframe.
- Ensuring the product is robust.
- Review if the product was developed on cost and on time.
- Assess how useable the system is by the end user
User interface
GUI Advantages - type of interface that allows staff to interact with a computer system through graphical icons:
- Intuitive for staff
- Easy to navigate for non specialist staff
- Uses Windows, Icons, Menus and Pointers which staff may be familiar with
- No complicated commands for staff to learn
- No need to be a proficient typist
GUI Disadvantages
- Requires a large amount of memory so increased costs
- Is processor intensive, so increased costs
- GUIs take up a much larger amount of hard disk space than other interfaces so increased costs
Command Line Interface (CLI) Advantages - Text based, allows communication with computer system through commands
- Quicker to type commands so staff can continue with other tasks
- Quicker to input commands as shortcut keys can be used again saves staff time
- Little memory and processing power needed compared with other interfaces saving on cost
- Staff members who have memorised the commands find it efficient to use
Command Line Interface (CLI) Disadvantages:
- Confusing for staff who have never used a command line interface
- Commands have to be typed precisely. If there is a spelling error the command will fail frustrating non specialist staff members
- A large number of commands need to be learned – adds training costs
- Not suitable for a novice/difficult for new staff to learn
Managing Resources
- Communicates with and sends data output to a printer / monitor / other valid output device
- Communicates with and receives data input to a keyboard / mouse / other valid input device
- Manages network communication
- In spooling, data is stored on hard disk / in memory / stored in a queue / in a buffer
- Manages backing store by ensuring that data is stored and can be retrieved correctly from any disk drive
- O/S creates and maintains a filing system such as FAT or NTFS
- Organise files in a hierarchical directory structure
- O/S offers compression which can be used to save disk space
- The O/S manages memory (RAM) by ensuring all programs and data including
itself is stored in correct memory locations/do not try to occupy the same memory location - The O/S manages memory (RAM) by ensuring all programs and data have enough memory allocated
- The O/S can utilise virtual memory when not enough memory (RAM) is available to run a program
- Ensures different processes can utilise the CPU and do not interfere with each other or crash
- On a multi-tasking O/S, the O/S ensures that all tasks appear to run simultaneously
Processes - a process is any task the computer is performing; simultaneous processes may request processor time, and the operating system allocates this time
Memory - loading data and instructions into RAM when needed and unloading them when no longer needed; ensuring processes do not use memory they are not permitted to use
Backing store - allocating physical disk space as files are added, edited or deleted; providing a hierarchical, searchable structure that users can interact with
Peripherals - maintaining a system of drivers (software that allows external devices, such as printers); facilitating communication between these peripherals and the computer
Off the shelf software
Off-the-shelf
- Cheaper. The development costs are spread across a large number of users, so
you pay much less than it would cost to build the same software from scratch.
- Available immediately. The development work has already been done, so all you need to do is set up the software and start using it.
- Lower training costs. If it is a commonly used package, users and I.T. staff may already be familiar with it, saving on learning time and training costs. Or, there may be pre-existing training materials and courses that you can leverage.
- Community support. If the software is popular, there may be books, articles,
forums and online communities offering support and advice to help you learn or resolve any issues. - More functionality. Off-the-shelf software often has more functionality, because the developers try to meet the requirements of as many users as possible. (There may even be functionality you didn’t realise you need!)
- Upgrades. The vendor will continue to develop the software, so you will likely get
upgrades for free or at a reduced cost, whereas in bespoke software you don’t get
anything new unless you pay for it to be built. - Compromise. You may have to compromise on your requirements – it is unlikely you will find ready-made software that does everything you need it to, exactly how you want it to.
- May be overly complicated. The software may include functionality that you don’t need, as it is trying to meet the different requirements of a number of users. This can make it more difficult to learn and use.
- You are not in control. The vendor’s plans for the future may not always fit with your own. As a single customer amongst many, you may not be able to get the features you want implemented.
- May be general e.g. Word Processing or specific e.g. Stock Control
Bespoke
Bespoke
- Tailored to you. The software is developed and built to meet your specific requirements, ensuring that you get software that works exactly how you need it to and delivers the results you want.
- More flexible. A bespoke system can evolve over time to match your changing requirements.
- No per-user fees. If you own the software, you won’t have to extra per-user fees as your business grows.
- Not tied in. You own the intellectual property, so you are not tied to a specific vendor that could potentially disappear at any time.
- Competitive advantage. As your competitors won’t have the same software, it could give you a competitive edge. An effective software package can make a company work more efficiently, improve their performance and have a positive impact on customer satisfaction levels.
- Higher initial costs. It will cost more at the beginning, as you have to pay the development costs.
- Takes longer. Depending on the size and complexity of the software, it may take months or even years to develop.
Compression
Compression
- When a file is compressed the file size is made smaller (and the amount of data may be reduced)
- To send as an email attachment
- Upload to a web site
- Save storage (disc, solid state, optical, server) space
Roles of GUI
Typical roles of the operating system in providing a graphical user interface:
- Provides user with a pointer / avoid text input
- Allows customisation of interface e.g. change desktop colours / layout
- Allows access to system settings such as hardware
- Allows copying / deleting / moving / sorting / searching of files or folders
- Allows creation of shortcuts
- Allows user to have more than one window open and to switch between tasks (programs/windows)
- Provides user with a menu-driven interface
- Provides user with error/warning/help messages
- Provides user with context sensitive help from library or on-line
File attributes
File attributes
- read only
- archive
- hidden
- system
Lossy compression
- Data compression reduces the file size
- When compressed files are decompressed they do not give back the original data, i.e. data is lost
- Because lossy compression cannot be decompressed to yield the exact original data, it is not a good method of compression for critical data, such as textual data
- It is most useful for digitally sampled analogue data, such as sound, video, graphics or images
- Some examples of lossy data compression algorithms are JPEG, MPEG, and MP3.
- Algorithms for lossy compression vary, but many use a threshold level truncation. /suitable lossy data compression example
Managing resources and providing interface
Interface
- Provides user interface with meaningful icons / avoid text input / drop-down menus
- Can provide a command line interface
- Allows customisation of interface e.g. change desktop colours / layout
- Allows access to system settings such as hardware
- Allows copying / deleting / moving / sorting / searching of files or folders
- Allows creation of shortcuts
- Controls security using passwords or access permissions
- Allows user to have more than one window open / Allows user to switch between tasks (programs/windows)
- Provides user with error/warning/help messages
Resources
- Communicates with and sends data output to a printer / monitor / other valid output device
- Communicates with and receives data input to a keyboard / mouse / other valid input device
- In spooling, data is stored on hard disk / in memory / stored in a queue / in a buffer
- Manages backing store by ensuring that data is stored and can be retrieved correctly from any disk drive
- O/S creates and maintains a filing system such as FAT or NTFS
- Organise files in a hierarchical directory structure
- O/S offers compression which can be used to save disk space
- The O/S manages memory (RAM) by ensuring all programs and data including itself is stored in correct memory locations/do not try to occupy the same memory location
- The O/S manages memory (RAM) by ensuring all programs and data have enough memory allocated
- The O/S can utilise virtual memory when not enough memory (RAM) is available to run a program
- Ensures different processes can utilise the CPU and do not interfere with each other or crash
- On a multi-tasking O/S, the O/S ensures that all tasks appear to run simultaneously
Modes of operation for processing data
- Example: Batch processing
- Example: payroll / utility billing
- Time sheets are collected for e.g. a monthly operation etc.
- Process is carried out with no user interaction
- Batch processing may avoid using computer resources at times when demand is high /off-peak
- Errors are stored in a file for later use and not dealt with as they occur
Input methods: - Scanning of sheets for batch file
Output method - Printing of payslips/electronic payslip sent
- Example: Real-time processing
- Example: nuclear power station to control reactor temperature by continuously monitoring the
temperature which is input to the system. - These Inputs are processed very quickly
- Processing needs to be quick enough to deliver output in time
- Output adjusted accordingly
- This means that accidents can be avoided.
Input methods: - Sensor (e.g. temperature sensor)
Output method - Adjust temperature/sprinkler/alarm/actuator
- Example: Real-time transaction processing
- Example: theatre selling tickets
- A seat is booked and the record is updated very quickly
- Record is locked during update
- Availability very quickly decreases by one
- This avoids double booking a seat.
Input methods: - keyboard
Output method: - Automated email
Managing Printers Using Spooling
- Data is stored on hard disc/in memory/stored in a queue
- Document is printed when printer is free/in correct order
- Benefit of spooling – user can carryon working/log off when waiting for job to print.
