Paper 2 - questions based on past papers

• State the purpose of the start bit in asynchronous serial transmission (1 mark)

  • Start the receiver clock ticking
  • Synchronise the clock in the receiver to the transmitter clock // bring the clock in the receiver into phase with the clock in the transmitter
• State the purpose of the end bit in asynchronous transmission (1 mark)

  • Provides time for the receiver to process/transfer the received data
  • Allows the (next) start bit to be recognised
• Describe two functions of an operating system (2 marks)

  Possible content:

  • To hide the complexities of the hardware from the user
  • To handle interrupts and to call the appropriate interrupt handler when an interrupt occurs
  • To allocate memory/RAM to processes
  • To allocate processors/cores to processes, to schedule processes
  • To manage communication between processes and I/O devices
  • To allocate space on storage devices to processes
  • Manage installing/updating software (may include automatic updates)
  • Manage power consumption/use of battery
• State two reasons why values stored using a floating point representation are usually stored in normalised form (2 marks)

  • Maximises precision/accuracy for given number of bits
  • Unique representation of each number//simpler to test for equality of numbers
• Compare how peer-to-peer networking and client-server networking work (3 marks)

  Possible content:

  Peer-to-peer networking: resources stored on/shared from any computer, each device has equal status, no centralised management of security (security can be managed individually on each computer)

  Client-server networking: one or more computers nominated as servers - the rest are clients, reliance on central server (must be turned on to allow clients to access resources), hardware and software on servers can be optimised for providing resources
• Describe the main purpose of the DNS system and how it works (3 marks)

  • The purpose of the DNS system is to map Fully Qualified Domain Names to IP addresses.
  • DNS servers work by storing a database of FQDNs and corresponding IP addresses.
  • The DNS is a distributed database of mappings.
  • Individual mappings are only known by some DNS servers.
  • DNS servers are organised into a hierarchy
  • If one DNS server cannot resolve a lookup, the query will be passed to another DNS server.
  • DNS servers support load distribution by returning one IP address from a list.
• Describe the advantages of using MIDI to represent music instead of using sampled sound (3 marks)

  • Using MIDI, it's easy to change the characteristics of the music and it can be modified at note level.
  • More compact representation
  • Simple method to compose algorithmically
  • Musical score can be generated directly from a MIDI file
  • No data lost through sampling
  • The MIDI file can be directly output to control an instrument/device
• Describe the principles of operation of an SSD (4 marks)

  • Data is stored electronically
  • Data is stored in floating gate transistors//transistors that do not lose their charge/state when power is no longer applied//electrons are trapped between oxide layers
  • Presence/absence of trapped electrons indicates 0/1
  • NAND/flash memory is used
  • Data is organised into pages/blocks
  • When writing to an SSD, you have to write to a whole block
  • A block needs to be cleared before you can write to it
  • Controller manages the organisation/reading and writing of the data
• Explain why a laser printer with a wireless network adapter is likely to be a suitable choice of printer for a small office (3 marks)

  • It will be advantageous to have a wireless printer as the employees may bring in their own devices and want to print using them.
  • Low cost per printed page (toner is cheaper per page than ink)
  • High speed
  • Toner will not dry out like ink
  • High resolution output
• Describe the principles of operation of a laser printer (6 marks)

  • Bitmap of image built in memory from page description
  • Negative charge applied to photosensitive drum
  • Laser beam directed at drum
  • Mirror is used to direct laser beam
  • Where laser strikes drum, charge is neutralised/reversed/cancelled/discharged
  • Negative charge applied to toner
  • Toner sticks to drum based on charge//where the laser struck
  • Paper passed over drum and toner transfers to it
  • Positively charged transfer roller assists transfer from drum onto paper
  • Heater fuses toner onto paper
• Explain why the relative error is usually considered to be a more important measure of error than the absolute error (1 mark)

  • The effect/impact of an error depends on its size relative to the number that should be represented.
• Describe the role of the control unit (3 marks)

  • To marshal/control the operation of the fetch-execute cycle
  • Controls fetching/loading/storing operations
  • Determines the type of an instruction
  • To execute (some) instructions
  • To synchronise the operation of the processor
  • To send control signals/commands to other components; To control the transfer of data between registers
  • To handle interrupts