paper 2 questions Flashcards
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
Explain how the External Router will have been configured so that the web server can
be accessed by computers outside the network.
Traffic arriving on the HTTP(S) port
Must be forwarded (by the External Router) to the IP address of the Web Server
Describe the principles of operation of an optical disk drive that is used to read data
from an optical disk such as a CD-ROM or DVD-ROM
(Low power beam of) laser / light is shone at disk
Light is focussed on spot on track
light is reflected back from disk
Amount of light reflected back is measured
Disc spins at constant linear velocity
Data is stored on one/spiral track
Continuation of land/pit reflects light whereas transition between land and pit scatters light
Transition between land and pit indicates a 1 and continuation of land/pit
represents 0
USB Flash Drives (a type of SSD) are a more popular choice for transferring files such
as images and word processed documents from one computer to another than CD-Rs
(a type of optical disk).
Explain why this is the case.
Flash drives can have a higher (storage) capacity
State two reasons why database designs, such as this one, are usually normalised
Minimise data duplication
Eliminate data redundancy
Explain some of the challenges that face legislators in the digital age.
Information can be combined/processed/transferred in ways that were not previously possible
Technology evolves quickly (so difficult for law to keep up with changes)
Some crimes may be committed by states rather than individuals
Describe what an ordinal number is and what an ordinal number would be used for in
the context of this array.
Shows order
The ordinal numbers would represent the position of the values in the array
Describe two security measures that the family should put in place to ensure that the
wireless access point is secure and explain how these security measures will make
wireless connections to the access point more secure.
Use WPA (WiFi Protected Access)/WPA2 To encrypt transmission
Encrypt transmissions so that if intercepted cannot be read by someone who doesnot have the key
The network uses the CSMA/CA access method with Request to Send/Clear to Send (RTS/CTS).
A computer on the network has data to send to another computer. Explain how the CSMA/CA access method with RTS/CTS will be used during this transmission
- computer with data to send monitors/listens for (data signal)
- if (data) signal present transmission in progress then continue to wait
- when no (data) signal present computer sends a Request to Send / RTS
- two computers could start transmitting simultaneously if they both detect there is no data signal
- receiver responds (to RTS) with a Clear to Send signal
- RTS/CTS signal blocks any other transmissions from nodes in range
- when CTS received then start to transmit
- if CTS not received continue to wait
- receiver sends acknowledgement after (all) data received
One characteristic of a data set that might result in it being classified as Big Data is that it contains a variety of different forms of information.
Describe two other characteristics that might result in a data set being classified as Big Data
There is a high volume of data (to process)
The data is must be processed at high velocity
what is the operating system responsible for
resource management
Describe two different types of resource management that an operating system is
responsible for
Allocate processors to processes
Allocate memory to processes
SMTP protocole
To send/receive emails
POP protocole
retrieve/manage emails on the server
SSH protocle
provides a secure/encrypted
connection for remote management
HTTP protocol
so that technicians can access web-based control panels
Explain how the transport layer of the TCP/IP stack determines which application layer software on the server should deal with a received request.
The transport layer will use the port number to determine which server should deal with the request
Describe one function of the network layer of the TCP/IP stack
Adds source IP to packets
Explain the key difference between lossless and lossy compression methods
The original data can be fully recovered if lossless compression has been used
Explain how text could be compressed using a
dictionary-based method.
A dictionary is built that maps sequences of characters in the
text onto tokens
The (sequences of) characters in the text are then replaced by
the corresponding tokens in the dictionary
Explain why dictionary-based compression is not very effective for compressing small amounts of text for transmission.
For small pieces of text there is little repetition (and so the compressed text will be similar in size to the original)
A student has written a computer program using an imperative high-level
programming language. The program could be translated using either a compiler or an interpreter.
Describe the steps that must be completed to translate and execute the program.
Your description should include:
* why translation is necessary
* the differences between how a compiler and an interpreter would translate the
program
* how the machine code instructions that are used to carry out the program will be
fetched and executed by the processor from main memory.
Processor can only execute machine code instructions
Compiler analyses program as a whole
Interpreter analyses program on a line-by-line basis
Compiler produces object code
Interpreter calls subroutines within its own code to carry out commands
Contents of Program Counter transferred to Memory Address Register
Address bus used to transfer this address to main memory
The control unit decodes the instruction
If necessary, data is fetched
If necessary, data is stored in memory
Describe an example of a problem that could occur if no system were in place to
manage concurrent access to the database
Two users edit a record simultaneously
One user writes the record then the other user writes the records
One user’s update is lost
record locks
when a user starts to edit a record an lock is set on the record
Other users cannot edit the record until the lock is released
timestamp ordering
Timestamps are generated for each transaction
Database records timestamp of last write transaction for each record
Explain the difference between asynchronous and synchronous communication
Asynchronous: Receiver and transmitter are not synchronised by a common clock
Synchronous: Receiver and transmitter continuously synchronised by a common clock
It is proposed that the communication system is modified so that:
* a majority voting system is used instead of the parity bit
* Unicode is used to encode the characters to be transmitted instead of ASCII.
Discuss the improvements that will occur in the communication system as a result of
these changes and any disadvantages that will result from them.
Errors can (sometimes) be corrected as well as detected
Multi-bit errors can be detected
A greater range of characters can now be transmitted
Each character will require more bits
Each bit will be sent multiple times
transmissions will take longer
A different computer system has a wider data bus; this will speed up the execution of
programs.
Explain how the wider data bus has resulted in this effect.
Increase the number of bits
Discuss the advantages and disadvantages of representing an image as a vector graphic instead of as a bitmap.
In your answer, include an example for which it would be most appropriate to use a vector graphic and an example for which it would be most appropriate to use a bitmap.
Individual parts of the image can be edited independently
The parts of the image can be enlarged without loss of quality
If an component is deleted, the software knows what is behind it
Can represent images with complex textures
Can represent images that are not composed of regular shapes
Images captured from nature
Explain what it means for a cipher to be described as being computationally secure.
The cipher cannot be cracked in a useful amount of time
Explain what the key exchange problem is, in relation to a symmetric cipher
How to pass the key to the receiver
Without it being intercepted
A message is to be transmitted from computer A to computer B. The message will be encrypted using asymmetric encryption. To enable computer B to authenticate that the message was sent by computer A, a digital signature will also be sent with the message.
Explain how computer B will decrypt the message and verify that it was sent by computer A.
In your response you should refer to the specific keys that will be used in this process
private key is used to decrypt the message
The message is rehashed
public key is used to decrypt the digital signature
if both hashes match then the sender can be authenticated
Explain the principles of operation of an ADC.
Amplitude of signal at each sample point measured
Measurement coded into a fixed number of bits
Advantage of floating point
a floating point system can represent numbers with a greater range than a fixed point system
can represent numbers much closer to zero
can represent much larger numbers
Advantage of fixed point
a fixed point system can represent (some) numbers more precisely than a floating point system
Calculations can be performed more quickly
Represents all numbers to a constant level of accuracy
When the decimal value 28.25 is converted into binary using this floating point system, a rounding error occurs.
Explain:
* why a rounding error has occurred, and
* what the system might do when the value 28.25 is converted into binary.
There are not enough bits in the mantissa
It could be rounded to the nearest representable value
Avoid/reduce bottleneck of single data/address bus(es)
reduces delays waiting for memory fetches
Avoids possibility of data being executed as code
describe the fetch part of the fetch execute cycle
copy the contents of the program counter into the memory address register
increment the value into the program counter
fetch the instruction from the main memory and store in the memory buffer register
copy the contents of the memory buffer register into the current instruction register
Describe the role of interrupts
Allows the currently executing process to be suspended
So that a device that needs the attention of the processor can be dealt with
Explain why the volatile environment (the contents of registers) must be saved before an interrupt is serviced.
So that the currently running process can be returned to
As the interrupt will change register values
Explain the relationship between hardware and software
Software executes on the hardware
CRUD
Create, Retrieve, Update, Delete
REST
allows JavaScript to communicate with the server using the HTTP
protocol
The database is connected to the web browser using REST
example of what XML looks like
<Properties>
<Property>
<PropertyID>8026</PropertyID>
<HouseNum>12</HouseNum>
<Street>Chester Drive</Street>
<Bedrooms>4</Bedrooms>
</Property>
<Property>
<PropertyID>9034</PropertyID>
<HouseNum>23a</HouseNum>
<Street>Castle Street</Street>
<Bedrooms>5</Bedrooms>
</Property>
</Properties>
State two reasons why it could be argued that JSON is better than XML
More compact
Quicker to parse
State one advantage of using the DHCP system
Reduces the need for expert knowledge when configuring a host
Reduces the time required to configure hosts
Explain how two or more computers connected to the Internet can have the same IP address and still communicate with each other
The computers have private IP addresses
as data passes onto Internet, private IP address replaced with public IP address of router
Explain four different ways that a firewall can protect computers on a LAN
Block/allow specific ports
Block/allow (traffic from) specific IP addresses
Act as a proxy server
Identify unusual behaviour from a host
Explain how:
* Computer A will use a subnet mask to determine whether or not it can send the packet directly to Computer B across the LAN or if the packet must be sent via the Internet
* the packet will be routed across the Internet
* the checksum can be used to determine if the received packet has been changed during the transmission
Determining if on LAN:
AND operation of subnet mask with Computer A’s IP address
AND operation of subnet mask with Computer B’s IP address
result (of each AND operation) is the network/subnet ID
network/subnet IDs compared
as they are different, then packet must be sent via router
Router:
path to take selected by each router
route may change as a result of eg congestion
route determined using the IP address
checksum:
checksum produced when packet transmitted
checksum calculated from packet contents
checksum transmitted with packet
Explain why the warehouse owners might prefer the individual products to be identified using RFID tags
the RFID tags could be read without removing products from their pallet;
RFID tags can be read from a distance (than barcodes)
Explain why the product manufacturers or supermarket owners might prefer the individual products to be identified using barcode labels
Barcodes are cheaper than RFID tags
Higher cost of RFID tags would be added on to prices
Describe how an RFID reader would read the ProductID and ItemID values from RFID tags as pallets are delivered and explain how this data could be used to update the database table that stores details of the products that the warehouse has in stock
RFID scanner sends signal;
Signal induces current in RFID transponder
RFID transponder sends data by radio
RFID signals processed into a format suitable for querying the database
query used to check if there is already a record for the product in the database
Explain what is meant by immediate addressing
The operand is the value that the instruction should use
Explain what a higher-order function is
A function that takes a function as an argument
and/or returns a function as a result
laser printer
bitmap of image built in memory from page description
charge applied to drum
laser beam directed at drum
mirror is used to direct laser beams
where laser strikes drum charge is discharged
charge applied to toner
toner sticks onto where the laser struck
paper passed over drum and toner transfers to it
positively charged transfer roller assists transfer of toner to paper
heat fuses onto paper
four drums are are required for colour printing
