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Describe how an instruction is fetched from main memory during the fetch stage of the fetch-execute cycle.
• Contents of Program Counter transferred to Memory Address Register • Address bus used to transfer this address to main memory • instruction transferred using the data bus • Contents of addressed memory location loaded into the Memory Buffer Register • Transfer content of Memory Buffer Register to the Current Instruction Register
During the decode and execute stages of the fetch-execute cycle the instruction that is being processed is stored in the CIR. Explain why the instruction could not be processed directly from the MBR.
• To carry out the instruction other data may need to be fetched • Further memory fetches would overwrite the contents of the MBR
Explain why the Harvard architecture is sometimes used in preference to the von Neumann architecture.
Instruction and data can be accessed simultaneously
State two conditions that must be met for the Vernam cipher to offer perfect security
The key must be (truly) random The key must not be reused
Explain the difference between a symmetric and an asymmetric cipher system
Symmetric: The same key is used to encrypt and decrypt Asymmetric: Different (but related) keys are for encryption and decryption
calculate bit rate
baud rate x bits
relationship between bit rate and bandwidth
bit rate is directly proportional to bandwith
Explain why serial communication is more appropriate in this instance than parallel communication
• Data skew might occur if parallel communication used • To avoid problems of cross-talk
Explain the general purpose of a D-type flip-flop
Used to store state
inputs other than data signal for d-type flip flop
Clock Used For: State of data input is stored
State the purpose of the operand part of an instruction and explain how the addressing mode is related to this
An operand is a value that will be used by an operation The addressing mode indicates how the value in the operand should be interpreted
Discuss the advantages and disadvantages of programming using a high-level language compared to programming using assembly language
Program code is easier to understand Faster development time Programs are (more) portable Language is problem-oriented
Explain what a higher-order function is
A function that takes a function as an argument
calculate storage space
Storage Space = (Sample Resolution) x (Sample Rate) x (Duration) x (Number of Channels) / 8
The highest frequency component in the sound that is being sampled is 14 500 Hz. The sample rate of 20 000 Hz is not high enough to enable a faithful reproduction of the original sound from the sample. Explain why this is the case, justifying your response
the sample rate must be at least twice the frequency of the (highest frequency component in the) original signal 20 000 is less than double of 14 500
Explain how MIDI represents music and the advantages of using MIDI for representing music instead of using sampled sound.
Music represented as sequence of MIDI (event) messages MIDI messages are usually two or three bytes long pros: More compact representation Easy to modify
Explain the difference between a physical topology and a logical topology
Physical: The physical layout of the connections Logical: How the data flows around a network
Explain the differences between client-server and peer-to-peer networking
Client-server: Resources stored on the server Clients access resources from server Peer-to-peer: Resources stored on each individual computer Computers communicate directly with each other
Between 2008 and 2010, a company that was gathering data for an online mapping system, using cars fitted with cameras and WiFi equipment, collected some information that was being transmitted on personal WiFi networks. The company apologised for doing this and an investigation found that a small number of software developers had been responsible for adding this functionality to the mapping system data collection software. In the context of this example, discuss: * how it was possible for this data to be collected. * what steps the owners of the networks could have taken to prevent the data from being collected.
WiFi signals can travel outside of property Any WiFi receiver in range can read the data packets No need to physically “tap” into a WiFi connection, unlike a cabled connection A protocol that does not encrypt the transmissions may have been used Use a protocol that encrypts data transmissions Disable broadcast of SSID to make network harder to identify Limit power of transmitter so data does not travel outside premises Use cabled network instead of WiFi
Describe how a vector graphic is represented.
Image is represented as objects Properties of objects are stored
Describe how a row of pixels could be represented in compressed form by using run length encoding.
A run is a series of pixels of the same colour Pairs of values would be stored which would consist of a run length and the colour of the pixels in the run
why might a less complex image with less colours be compressed more effectively than an image with more colour
the image (in the second figure) contains a lot more different colours the additional run length data may cancel out the reduction in storage of pixel colour data
Employees at a bank use client computers to access data that is stored on a box database server. The database server uses software to query and modify data stored in a database on hard disk drives. It returns the results of these queries to the clients over the bank’s computer network. The performance of the system is unsatisfactory: the time-delay between a client sending a query to the server and the client receiving the results is unacceptably long. Explain how the performance of the system might be improved. You should consider the following factors that might be affecting the performance: * the hardware of the server * the design of the computer network * the database and software running on the server.
Replace the processor with one which has more cores Replace the processor with one which has more cache memory Replace the processor with one which runs at a faster clock speed Replace the network cable with cable that has a higher bandwidth Replace any wireless/WiFi connections with wired ones Use a star topology Use a non-relational database system Distribute the data across multiple servers Try to reduce the amount of other software that might be running on the database server at the same time
Explain: * the purpose of the DHCP system * why the DHCP system is used * what will happen during this communication
to allocate IP addresses to hosts reduces the time required to configure hosts Host sends request to discover a (DHCP) server DHCP servers offer configuration to host