CS Paper 2

• System software manages the computer hardware / application software while application software is for end-user tasks
• Functions of the Operating System

  • Memory management
  • Processor management
  • Input / output management
  • Managing storage
  • Managing security
  • Managing applications
• Memory management


  • Manage the computer's memory
  • Control which parts of memory are being used by the process
• Processor management

  • Manage the computer's CPU
  • Schedule which processes are to be executed
• Input / output management

  • Manage input / output devices
  • Manage the installation of device drivers
  • Handle peripheral device interrupts
  • Allow the computer to communicate with the outside world
  • Control network communication
  • Allow devices to send and receive data
• Managing storage

  • Manage secondary storage devices (SSDs)
  • Load data and programs into the computer's memory
  • Manage storage space (disk quotas)
  • Ensure that storage space is allocated fairly and efficiently to specific tasks \ users
• Managing security

  • Perform user authentication
  • Protect against malware
  • Block access to specific vulnerable operations or system areas
• Managing applications


  • Control access to applications
  • Prevent users or processes using unauthorised programs
  • Allow users or processes to use authorised programs
  • Control application access
  • Prevent / allow an application access to data (or devices)
• How do interpreters work?

  • needs to be translated each time, no machine code
  • translates on line at a time
  • runtime error forces it to stop
• HLLs


  • in built data structures, easier to manage and manipulate data
  • modules such as subroutines/functions, easier to code
  • in built functions, compact code, quicker
  • may be problem oriented
• HLL programs

  can be written in less time, as less statements needed, as each statement is equal to numerous instructions
• HLL programs


  easier to understand bcs more English-like | more modularisation
• One HLL instruction


  Is equivalent to many LLL instructions and there is a one-to-one correspondence between LLL instructions and instructions that the processor can directly execute
• LLL programs

  Can be executed more quickly or use less memory as conversion from HLL to LLL does not always produce optimal code or as the programmer can hand-optimise efficient programs in an LLL
• Advantages of cloud storage:

  
  

  •  easier to access anywhere 

  •   easier to share anywhere

  •  increase potential storage

  •   to allow concurrent access/collaboration;

  •   cloud storage is automatically backed up by the host;

  less physical storage needed on PC, ∴ lower costs
• Improving CPU speed:

  -> clock speed ∴ more instructions happen per second ∴ more FDE cycles per second

  -> processor cores ∵ more instructions simultaneously ∴ more FDE cycles simulatenously

  -> cache size ∵ data held close to CPU ∴ little distance travelled ∴ instructions happen quickly
• Blagging

  This is where a victim is tricked/persuaded by a fraudster to give their details or payment information for a false reason/purpose;
• social engineering: Manipulating / fooling people into revealing confidential information / login details / bank details
• Access rights: restrictions on what users can do.

  if misconfigured, users can delete or read data they should not be able to
• Pharming


  Setting up a fake website that looks like an official website for a reputable organisation / company (to try and harvest personal details)
• Shouldering / shoulder surfing


  Observing a legitimate user entering (security) data into a computer system
• Baiting


  Leaving a malware infected portable storage device around hoping that a legitimate user will insert it into the computer system
• blagging


  Persuading (often by use of a faked scenario) legitimate users to give personal data
• To reduce risks from

  • Phishing: allow emails only from known sources
  • Pharming: web filters
  • Shouldering: careful placement of terminals
  • Baiting: lock down systems so portable storage devices are not usable
  • Blagging: use of security details which cannot be accidentally divulged eg biometric measures
• General strategies for reducing the risks from social engineering

  • Train users
  • Making use of appropriate security protocols for handling sensitive data
  • Performing frequent (unannounced) tests of security measures
• Solid state storage

  • Non-volatile
  • Portable
  • Durable due to lack of moving parts
  • Stores data electrically in silicon chips
  • Provides faster performance compared to magnetic devices
• Magnetic devices (e.g. hard disk drives)

  • Use magnetic fields to store data on spinning disks
  • Cheap
  • High-capacity
  • Durable
  • Susceptible to damage from drops and magnetic fields
• Optical devices

  • Use lasers to read and write data on spinning discs divided into tracks
  • Lands and pits represent binary '1's and '0's
  • Different types of optical media (ROM, R, RW) with different capabilities for writing and rewriting data
• Advantages of computer networks:

  1. File sharing
  2. Hardware sharing
  3. Communication options
  4. Roaming access
  5. Centralized maintenance and updates
  6. Centralized security
  7. User monitoring
  8. Customizable access levels

  Disadvantages of computer networks:

  1. Cost
  2. Management requirements
  3. Spread of malware
  4. Hacking potential
• Application layer


  Applications such as web browsers and email programs operate at this layer. Protocols such as HTTP, HTTPS, SMTP, IMAP and FTP operate at this layer.
• Transport layer


  This breaks down the message into small chunks (packets). Each packet is given a packet number and the total number of packets. This layer sets up the communication between hosts, using protocols such as TCP and UDP.
• Internet layer

  This adds the sender's and recipient's IP addresses to the packet, and packages the data to make it ready for transmission. The internet layer also routes the packets across the network.
• Link layer


  The network interface card/controller (NIC) and operating system drivers are at this layer.
• The Computer Misuse Act 1990 was introduced in response to a rise in computer hacking
• In 2016, the government introduced the Investigatory Powers Act. 
• The 4 layers are:

  Application, Transport, Internet and Link
• Secure the backups

  • Store backups off-site
  • Ensure they are air-gapped to prevent malware access
• Block or remove email attachments or links


  Avoid opening unexpected email attachments or clicking on suspicious links
• Disable pop-ups


  Activate pop-up blockers and screen website options to prevent unwanted pop-ups
• Control software downloads

  Only download software from trusted sources to avoid potential security risks