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Craig n Dave, Advantage of Hard disk > Solid-state - hard disk has a…

- - - - Local area Network (LAN):
        
        Covers a small geographical area located on a single site.
        
        All the hardware for a LAN is owned by the organisation using it.
        
        LANs are wired with UTP cable, fire optic or wireless using Wi-Fi.
        
        Wide area Network (WAN):
        
        Covers a large geographical area, connecting LANs together.
        
        Infrastructure between the LANs is leased from telecommunication companies who own and manage it.
        
        WANs are connected with telephone lines, fibre optic cables or satellite links.
        
        Modes of Connection: wired and wireless
        
        Ethernet:
        
        A standard that has been around for many years.
        
        It has evolved as network topologies have evolved.
        
        Used for communicating on a wired LAN.
        
        Includes a number of associated protocols (rules for governing communications)
        
        Provides reliable, error free, fast communication between two points.
        
        Originally used in old style bus networks.
        
        Still used today is more modern star and mesh networks.
        
        Data is transmitted in frames which includes: preamble of bits used to synchronise transmission, start frame deliminator to signify the start of the data part of the frame, source and destination MAC address, the actual data, error checking information (cyclic redundancy check - CRC)
        
        Users location is limited by the need for a physical cable connection
        A set up relying on Ethernet relies on lots of cables, connections, ports and physical hardware which will affect cost
        
        Wireless connections (Wi-Fi and Bluetooth):
        
        Wireless connections are popular because it avoids the need to install cables.
        
        It is a portable connection.
        
        Bandwidth is lower than a wired connection
        
        Security is more of a problem than with wired connections
        
        An ever increasing number of home devices are making use of Wi-Fi.
        
        Ideal as running lots of cabling through a home is undesirable
        
        Wi-Fi is a common standard for wireless networks:
        
        Users can move around freely.
        
        Easier to set up and less expensive
        
        Convenient to use
        
        Can handle a large number of users.
        
        Transfer of information to social media is much easier.
        
        Speeds are slower than wired networks.
        
        Relies on signal strength to the wireless access point (WAP)
        
        Signal can be obstructed.
        
        Less secure than wired networks
        
        Range of 100 metres
        
        High bandwidth and power consumption compared to Bluetooth
        
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        The use of IP and MAC addressing:
        
        Every device on a network has a Network Interface Card (NIC)
        
        Every NIC has a Media Access Control (MAC) address
        
        It is used to route frames on a local area network (LAN)
        
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        Standards
        
        Standards in use: HTML and Web-pages:
        
        HTML is an example of an early standard adopted on the World Wide Web (WWW) for the displaying of web-pages in browsers.
        
        This is an example of an agreed standard in use.
        
        The need for standards:
        
        We need standards in computer science because otherwise software and hardware would never be able to communicate or work together
        
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      - Disadvantages of Networking:
        
        Increased security risks to data.
        Malware and viruses spread very easily between computers.
        
        If a server fails, the computer connected to it may not work.
        
        The computer may run more slowly if there is a lot of data travelling on the network.
  - - - Advantages:
        
        Easier to manage security files.
        
        Easier to take backups of all shared data.
        
        Easier to install software updates to all computers.
        
        Disadvantages:
        
        Can be expensive to set up and maintain.
        
        Requires IT specialists to maintain.
        
        The server is a single point of failure.
        
        Users will lose access if the server fails.
        
        Each computer is NOT responsible for its own security
        
        Server:
        
        Controls access and security to one shared file store
        
        Manages access to the internet
        
        Manages printing jobs
        
        Provides email services
        
        Runs data backups
        Client:
        
        Requests the service from the server.
        
        Peer-to-peer:
        
        A peer is a computer on a network and equal to all other peers
        
        Peer serve their files to each other
        
        Each peer is responsible for its own security and backups
        
        Peers usually have their own printers
        
        You can send print jobs to another peer to process, but that peer needs to be switched on to communicate with the printer.
        
        Hardware used to connect to a lan
        
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    - - Advantages:
        
        Very easy to maintain.
        
        Specialist staff are not required.
        
        Cheaper to set up.
        
        No expensive hardware required.
        
        No dependency on a single computer
        
        Disadvantages:
        
        The network is less secure.
        
        Users will need to manage their own backups.
        
        Can be difficult to maintain a well ordered file store
    - - Network topology: a given arrangement of all the elements that you need for networking.
        
        Historical network topologies:
        
        Bus topology - devices connected to a central backbone cable. If the backbone breaks all devices lose their connection
        
        Ring topology - devices connected by a ring cable. Has the same potential issues as the bus network with a main cable failure. A second ring can be introduced to prevent this issue , but this requires extra cable.
        
        Star Network Topologies:
        
        Most popular type of wired network
        
        Central switch
        
        All devices connect into the central switch.
        
        The switch is intelligent and makes sure traffic only goes where it is intended.
        
        If a single cable breaks only that computer is affected.
        
        The switch however is still a serious point of failure
        
        Full Mesh Network Topology:
        
        Every device is connected to every other device.
        
        Advantage is that if you get a break in any of the connections you can still route your traffic via another route.
        
        Disadvantage is that there is a lot more cabling and switch hardware required which will add to the cost for large networks
        
        Partial Mesh Network Topology:
        
        Multiple routes exist between different devices.
        
        However every device is not connected to every single other device.
        
        A compromise solution which lowers the amount of hardware needed compared to a Full Mesh network.
        
        E.g. the Internet
  - - - The number of users:
        
        Too many users or devices on the same network can cause the network to slow down if there is insufficient bandwidth for data.
        
        Transmission media:
        
        Wired connections have a higher bandwidth than wireless connections.
        
        Fibre optic cables have a higher bandwidth than copper cables
        
        The error rate:
        
        Less reliable connections increase the number of errors that occur when data is transferred.
        
        This means the data has to be resent until it arrives correctly.
        
        The signal quality of wireless connection is dependent on the range of devices from the wireless access point (WAP) and other environmental factors.
        
        The signal quality of the copper cables is determined by the grade of material used which reduces interference.
        
        The length of the cable is also a factor.
        
        Latency:
        
        The delay from transmitting data to receiving it.
        
        Latency is caused by bottlenecks in the infrastructure of the network.
        
        For example, by not using switches to appropriately segment traffic on a network
        
        Hardware such as switches and transmission media may not operate at the same speed
    - - Most well known WAN (Wide area network)
        
        A collection of interconnected networks spanning the world.
        
        Not the same as the world wide web which is just a service on the Internet
        
        Here we see a home network connected via a typical wireless router.
        
        The home router is connected to an Internet service provider (ISP)
        
        Our ISP is connected to the Domain Name server (DNS) and other routers on the backbone of the Internet.
        
        These routers are further connected to:
        
        Their own LANs.
        
        Other routers
        
        Servers
        
        Web servers and clients:
        1) URL request by browser made from user e.g. bbc.co.uk
        2) The browser sends the domain name to a Domain Name Server (DNS)
        3) The DNS maps the domain name to an IP address and returns it to the browser
        4) GET request for the webpage / resource is sent to the web server using the IP address
        5) The requested web page is returned to the client's web browser
        
        Web servers carry out many functions, but by far their most common is:
        
        Hosting websites
        
        Dealing with client requests e.g. HTTP gets requests for a page / browser resource.
        
        The webpage, stored as text (HTML,CSS,Javascript) is sent to the browser which uses rules to render it correctly for the user.
        
        The cloud:
        
        Servers can be used to store data and programs that can be accessed and used over The Internet.
        
        This is known as “The Cloud”.
        
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        Domain Name Server: maintains an index of mapped URLs to IP addresses and serve web pages
- - - - Common CPU components and their functions
        
        The CPU consists of the following components:
        
        Arithmetic Logic unit (ALU) : performs calculations and logical decisions
        
        Control Unit (CU): sends signals to control how data moves around the CPU
        
        Cache: provides fast access to frequently used data and instructions
        
        Registers: tiny, super fast pieces of onboard memory inside the CPU each with a very specific purpose
        
        Von Neumann Architecture
        
        The Von Neumann Architecture consists of:
        
        ALU,
        
        CU,
        
        Memory unit ( typically RAM)
        
        Inputs and outputs
        
        It is based on the concept of the stored-program concept
        
        Both instruction data AND program data are stored in memory in binary form
        
        there is no way to know if the pure binary held in memory is representing instructions or data by simply looking at it
        
        It contains the following registers:
        
        Program Counter (PC): holds the address of the next instruction in memory. Increments by 1
        
        Memory address Register (MAR) : holds the address of where data is to be fetched or stored
        
        Memory Data Register (MDR): holds the data fetched from, or to be written to memory
        
        Accumulator: Holds the results of calculations
        
        Embedded systems
        
        Embedded system: a computer system with a dedicated function that is part of a larger mechanical system
        
        Typical properties include:
        
        Low power consumption
        
        Small size
        
        Rugged operating rates
        
        Low cost per unit
        
        Examples:
        
        Traffic lights
        
        Domestic appliances: coffee machines, washing machines etc
        
        Factory equipment
        
        Engine management systems
        
        Hospital equipment
        
        The performance of a CPU is affected by various factors.
        Clock speed:
        Measured in Hertz (Hz)
        Number of cycles per second
        Modern processors operate at billions of cycles per second, Gigahertz (GHz)
        3.2 GHz clock speed = 3.2 billion instructions can be fetched per second.
        
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- - - - PRIMARY STORAGE:
        
        With the exception of ROM,all volatile (when we turn the power off to a computer,they lose any data being held).
        
        ROM is considered read only.
        
        Relatively small capacity compared to secondary storage.
        
        RAM is typically measured in gigabytes whereas secondary hard disks are often measured in terabytes.
      - SECONDARY STORAGE:
        
        All non-volatile, meaning that when we turn the power off, they are able to hold the data stored on them.
        
        Much larger storage capacity compared to primary storage.
        
        What is the point of Primary storage?:
        
        Primary storage has very fast access times compared to secondary storage which has very slow access times. Primary storage access speeds can be tens or hundreds of times faster than secondary storage.
        
        This speed of access is the main need for primary storage.
        
        RAM and ROM:
        
        ROM: Read Only Memory:
        
        Small piece of read only memory located on the motherboard
        
        Non-volatile
        
        Contains the very first instructions for the computer (bootstrap)
        
        Read only
        
        Software stored on the ROM is referred to as firmware.
        
        In some computer systems, ROM chips can be changed in order to change the program being executed. An example of this are game cartridges in portable entertainment systems.
        
        RAM: Random Access Memory:
        
        Temporary storage of instructions and data
        
        Holds information being executed by the processor
        
        Volatile
        
        Much faster than the hard disk.
        
        Read and write.
        
        Although the long-term storage is usually on the hard disk, it would be too slow to execute instructions from there.Therefore they are transferred from the disk to the memory first.
        
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- - - - Data interception and theft:
        
        The unauthorised act of stealing computer-based information from an unknowing victim with the intent of compromising privacy or obtaining confidential information.
        
        E.g. To sniff usernames and passwords
        
        Threats posed to networks
        
        Threats:
        -Malware,
        
        Phishing,
        -SQL injection,
        
        Brute force,
        
        Denial of service,
        
        People as a 'weak point' in secure systems (social engineering)
        
        Malware:
        
        Files are deleted, become corrupt or are encrypted.
        
        Computer crash, reboot spontaneously and slow down
        
        Internet connections become slow
        
        Keyboard inputs are logged and sent to hackers
        
        Brute force attack:
        
        Theft of data,
        
        Access to corporate systems
        
        Denial of Service (DoS):
        
        Loss of access to a service for customers
        
        Lost revenue
        
        Lower productivity
        
        Damage to reputation
        
        Data interception and theft:
        
        Usernames and passwords compromised
        
        Disclosure of corporate data
        
        Theft of data
        
        SQL Injection:
        
        Contents of databases can be outputted, revealing private data.
        
        Data in the database can be amended and deleted
        
        New rogue records can be added to the database
        
        People as a weak point:
        
        Many system vulnerabilities are caused by people being careless:
        
        Not installing operating system updates
        
        Not keeping anti-malware up to date
        
        Not locking doors to computer rooms
        
        Not logging off or locking computers
        
        Leaving printouts on the desk
        
        Writing passwords down on sticky notes attached to computers
        
        Sharing passwords
        
        Losing memory sticks / laptops
        
        Not applying security to wireless networks
        
        Not encrypting data
        
        Identifying and preventing vulnerabilities
        
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        Phishing:
        
        Accessing a victim's account to withdraw money, or purchase merchandise and services
        
        Open bank accounts and credit cards, cashing illegitimate cheques
        
        Gain access to high value corporate data
        
        Financial services can blacklist the company, resulting in damage to brand reputation
      - SQL injection:
        
        A technique used to view or change data in a database by inserting additional code into a text input box, creating a different search string.
        
        E.g. Smith " or " "="
    - - Denial of Service (DoS):
        
        Flooding a server with useless traffic causing the server to become overloaded and unavailable.
- - - - Hardware - how the output is produced
      - File management - The user will want to save what is in memory from time to time so that they don't lose their work when the power's switched off so the operating system also has to manage a file store. It has to make decisions about where files are going to be stored and where they are going to be loaded from again
      - Utility programs - e.g. encryption software compression software and defragmentation software. Some are built into the operating system to help maintain the computer
      - Device driver - the large array of additional peripheral hardware connected to computers are also going to operate in a very special way and therefore need some device drivers in order to translate operating system instructions into something that the hardware is actually going to understand.
        
        Types of user interfaces:
        
        Graphical user interface (GUI):
        
        Windows, Icons, Menus, Pointers (WIMP)
        
        Visual
        
        Interactive
        
        Intuitive - ideal for beginners
        
        Optimised for mouse and touch gesture input
        
        Command line:
        
        text based
        
        less resource heavy compared to a GUI
        
        more commands than a GUI
        
        Effcient
        
        For advanced users
        -Useful for automating processes with scripts.
        
        Menu:
        
        Successive menus presented to the user.
        
        Single options chosen at each stage.
        
        You often interact with them via buttons on a keypad
        
        Natural Language Interface:
        
        Responds to questions in spoken language
        
        Not always reliable
        
        Getting better all the time
        
        Operating systems part 1
        
        Multi-tasking
        
        Running multiple applications at the same time by giving each application a small time-slice of processor time
        
        This allows more than one program to be held in memory at a time, and data shared between them such as copy and paste.
        
        It also enables you to listen to music on your PC at the same time as word processing
        
        Memory management
        
        when programs are loaded, the operating systems decide where they are held in memory
        
        over time the memory becomes fragmented as programs are loaded and closed because they use different amounts of memory
        
        The operating system must keep track of different program fragments
        
        When the memory is full, the operating system uses virtual memory
        
        Device drivers
        
        Translates operating system instructions into commands that the hardware will understand
        
        Each peripheral needs a device driver
        
        Many are built into operating systems
        
        Operating systems part 2
        
        User management:
        
        Providing for different users to log into a computer
        
        The operating systems will retain settings for each user, e.g icons,desktops,backgrounds etc
        
        Each user may have different access rights to different files and programs
        
        A client server network may impose a fixed or roaming profile for a user and manage login requests to a network
        
        File management:
        
        Data is stored in files
        
        An extension to the file name tells the OS which application to load the file into
        
        The OS may present a logical structure of files into folders and allow the user to rename delete copy and move files
        
        Utility system software
        
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      - User - inputs the data
      - Application software - used by the user to accomplish a given task
      - Memory management - loading programs into memory so that they can be executed and managing the data of those programs in memory is not a trivial task, especially when combined with virtual memory, so the operating system has the manage the memory for the processor
      - User interface - application software involves a common user interface so that the user is interacting with the application software in a familiar and friendly way.
- - - - Ethics is not so much about whether something is legal or illegal but more about whether something is morally right or wrong
        
        Jumping ahead in a queue is not illegal, but morally it is deemed unacceptable in our culture
      - The internet presents many legal, ethical and cultural issues
        
        It has many benefits:
        
        Vast respiratory of knowledge
        
        Communication
        
        Education
        
        Research
        
        E-commerce
        
        It also has drawbacks:
        
        Increase in piracy
        
        Distribution of illegal images
        
        Offensive content
        
        Fraud
        
        Hate speech
        
        Dissemination of fake news
        
        Should the Internet be regulated?:
        Yes:
        
        The internet is no different to other media: radio, TV, newspapers etc
        
        The Internet has harmful and illegal content
        
        Children should be better protected
        
        Profit making organisations on the Internet should share responsibility or policing the Internet the have created
        No:
        
        Freedom of expression is an absolute right
        
        The Internet is different to other media because anyone can be an author or broadcaster
        
        The Internet grows too quickly for filtering to be effective
        
        Censorship is bad for democracy
        
        Parents should take more responsibility
        
        Privacy issues
        
        Schools often monitor Internet, emails, and general computer activity
        
        Companies often monitor their workforce's browser use and record their business calls
        
        Data is an incredibly valuable commodity
        
        Should smart devices be continually recording?:
        For:
        
        Data encryption makes it private
        
        Voice input is convenient: the next step in user interfaces
        
        Processing sound data allows for additional functionality
        
        Intelligence may save lives
        
        If you have nothing to hide then privacy is not an issue
        
        Data is not recorded for other purposes
        Against
        
        Invasion of privacy
        
        TV may also be taking video footage
        
        Data is sent over the Internet for processing
        
        The data may not just be used for the purpose intended
        
        Privacy issues of computer science:
        
        Number plate recognition
        
        Face recognition
        
        Electronic tagging
        
        Cell phone location and GPS technology
        
        Recording internet browsing history
        
        Retention of personal data
        
        Smart listening devices
        
        Cultural implications
        
        Positive effects of technology on culture
        
        In the developing world the rapid spread of technology , fuelled by the Internet, has led to positive cultural changes in developing communities.
        
        Easier, faster communication has contributed to the rise of democracy as well as working towards the alleviation of poverty
        
        Globalization can also increase cultural awareness and promote divsersity
        
        Negative effects of technology on culture:
        -Diffusion of technology must be carefully controlled to prevent negative cultural consequences.
        
        Developing countries risk losing their cultural identities and assimilating themselves into an increasingly westernised world
        
        Challenges of equality from the uneven distribution of technology within a country still remain
        
        Cultural influences of developers on software
        
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