PAPER 2 PAST PAPERS Flashcards
1
Q
Explain how unsigned binary integers can be converted to hexadecimal [2]
A
the bit pattern is split into sections of 4 bits, each section is converted to hexadecimal
2
Q
One advantage of using majority voting over a parity bit and explain how this advantage is achieved [2]
A
majority voting can correct as majority is taken as correct, can detect multiple errors as each triplet represents one and bit and error is identified per bit
3
Q
Describe the steps the ADC goes through [3]
A
takes samples of the signal at regular intervals, samples are quantised, each sample is assigned a binary value
4
Q
Explain why it is more appropriate for a band to save the song using lossless compression rather than lossy [2]
A
no data is lost during lossless compression, song can be reproduced identically to original with no loss of quality w lossless
5
Q
Explain the differences between an interpreter and a compiler [4]
A
compiler produces object code, interpreter does not, compiler translates whole source code, interpreter translates line by line, compiler will not produce an executable file if there is an error in code, interpreter will run program up until first error, compiler no longer needed to execute compiled program, interpreter is always needed
6
Q
A company is using a new processor in its latest microwave, why have they chosen to use assembly language rather than a high-level language [3]
A
may not be an interpreter for the chip as it is new, platform dependence is not relevant since code will only run on one type of device, for an interpreted solution the chip would have to incorporate an interpreter which would increase memory requirements
7
Q
Describe one difference between the way the Harvard and von Neumann architectures operate [2]
A
harvard uses separate memory/bus/address space while von neumann uses combined memory/bus/address space, for instructions and data
8
Q
Which type of computer architecture that is used for digital signal processing [1]
A
harvard
9
Q
Describe the steps involved in the Fetch-Execute cycle for the von Neumann [6]
A
fetch: contents of PC transferred to MAR,
address bus used to transfer to main memory
contents of addressed memory location loaded into MBR,
increment PC,
contents of MBR copied to CIR
decode: decode instruction hold by CIR,
control unit decodes instruction,
split into opcode and operand
execute: data is fetched or stored in memory if needed,
opcode identifies type of operation to be performed,
result stored in register,
operation performed by processor
10
Q
Explain the difference between direct addressing and immediate addressing [1]
A
direct addressing means that operand is the memory address/register number, immediate addressing means that the operand is the datum
11
Q
Describe two reasons why serial transmission might be preferred to parallel transmission [4]
A
parallel requires more wires so higher cost and more difficult to manage, parallel risk of data skew over long distances so limits transmission speed, parallel risk of crosstalk between wires so more chance of errors and limit transmission speeds
12
Q
Define bit rate [1]
A
frequency at which bits can be transmitted/transferred
13
Q
Define latency [1]
A
the delay between signal being transmitted and arriving
14
Q
Explain how disabling SSID broadcasting can increase the security of a wireless network [2]
A
SSID will not be visible when trying to connect to network so only users who know SSID of network can connect
15
Q
Explain how the use of a MAC address white list can increase the security of a wireless network [2]
A
MAC address is unique to every NIC and a whitelist only allows those MAC address that have been authorised to connect to the network
16
Q
Discuss legal ethical and cultural issues with Street View [9]
A
material may be of harm to children, requesting permission from any members of public, recording of adverts may lead to product placement, what harmful uses users might use the images for, dealing with copyrighted information, does google need permission to film in private buildings, may not be legal to film people without permission, copyrighted information caught may lead to legislation breach, ability to identify locations for crimes or terrorism, worldwide so need to consider worldwide legislation, offensive to cultures, pictures inside religious buildings may be inappropriate
17
Q
Describe how a laser printer prints an image to a piece of paper [6]
A
print drum coated in charge, printer generates bitmap of page from data, laser beams shone on print drum, laser is modulated, laser neutralises charge on drum where image is dark, toner given charge, toner transferred to paper, toner fused to paper
18
Q
In decimal, what is the most negative number that can be represented using 12-bit two’s complement binary integer? [1]
A
-2048
19
Q
Describe the difference between analogue and digital data [2]
A
analogue is continuous, digital is discrete
20
Q
State two advantages of representing music using MIDI instead of as sampled sound [2]
A
more compact representation, easy to modify notes, easy to change instruments
21
Q
What is encryption? [1]
A
convert a message into cipher text, requires key to decrypt
22
Q
Explain why the Vernam is a better choice than the Caesar cipher [2]
A
vernam is unbreakable as frequency analysis reveals nothing, more possible keys
23
Q
Which category of software does an operating system belong to?
A
system software
24
Q
State one resource that the operating system manages [1]
A
processors, memory, I/O devices
25
State one role of the operating system, other than resource management [1]
hide the complexities of the hardware from the user
26
What is the stored program concept? [2]
instructions are stored in main memory and fetched and executed serially by processor, programs can be moved in and out of main memory
27
Ella's program is compiled into an executable file but will not run on Josephine's because they have different processors. Explain why different processors may have caused this issue [2]
different processors will have different instruction sets, program is in machine code and is platform dependent
28
Why might a computer with one running at 3.2GHz complete tasks faster than one with fore cores running at 2.8 GHz [2]
a processor with clock speed of 3.2GHz may be able to execute instructions more quickly, where sequential processing is needed
29
Discuss the ethical legal and cultural issues that may arise from creating driverless cars to provide a taxi service [9]
developers have to take responsibility for accidents, program needs to make moral decisions, need to be protected from hackers, putting taxi drivers out of business, other businesses may follow suit putting people out of business, if a customer is ill the taxi will not be able to handle that, legal responsibility for accidents, if videos/images taken during driving, driverless cars would need to be advertised as safer and reducing congestion
30
Describe a digital image could be captured by a digital camera and compressed using run-length encoding [6]
light enters through lens on to sensor chip, each sensor produces an electrical signal, representing a pixel, ADC converts light intensity into binary data, colour filter applied, image is analysed to identify runs of same colour, colours and counts of pixel are stored
31
Describe the difference between a physical and logical topology [2]
physical: the physical layout/architecture of the cabling, logical: how data flows around a network
32
Explain the operation of a physical star topology [2]
every device is connected to central hub, every device sends data via central hub, hub sends packets of data to intended recipient only
33
A new bank is setting up an internal network, explain why it should implement a client-server rather than peer-to-peer [6]
servers would need to be accessible at all times, p2p may be turned off, needs to have centralised backups reducing cost and time taken to ensure data is secure, centralised security ensuring anti-virus are up to date ensuring maximum security
34
Explain why some compilers produce bytecode as the final output instead of executable code [1]
code may need to be run on multiple platforms so may need to be platform independent
35
Describe how bytecode programs are executed after the bytecode has been produced [2]
a virtual machine interprets bytecode an instruction at a time and runs necessary code to carry out command
36
Explain what is meant by the term imperative high-level language [2]
instructions are execute in programmer-defined order, describes how to solve a problem
37
Explain the difference between the set of natural numbers and the set of integer numbers [1]
integers include negative numbers, natural numbers do not
38
Explain the difference between rational and irrational numbers [1]
rational can be expressed as a fraction, irrational can not
39
Explain why programmers often use hexadecimal to represent bit patterns instead of binary [1]
more compact when displayed, easier for people to understand, lower likelihood of an error when typing in data
40
Explain why Unicode was introduced as an alternative to ASCII [2]
introduced to support a larger range of characters due to increased international communication
41
What is meant by the term hardware? [1]
the physical components of computer system
42
What is meant by the term software? [1]
instructions
43
Explain the key difference between system software and application software [2]
system software controls the operation of computer system, application software is for carrying out tasks that are user-oriented
44
When a processor writes data to the main memory it will make use of the address, control and data buses. Explain how each of these buses will be used during the write process [4]
address of memory to be written to is placed on address bus, data to be written is placed on data bus, signal to write is placed on control bus, control bus carries a clock signal to synchronise memory and processor
45
Explain why computers have both hard disks and SSD rather than just one [2]
magnetic disk drives are useful where large capacity needed, ssd have faster access speeds
46
Explain why it is faster to access data from solid state storage than from an optical disk [2]
no movable parts so no need for read/write heads to move to correct position, purely electronic so minimal latency
47
Explain why a peer-to-peer network may be better for three students sharing a house who have set up p2p for sharing files and playing multi-user games [2]
does not need central server, easer to maintain, probably wont need extra security or extra services provided by client-server
48
Define the term protocol [1]
a set of rules
49
Define the term baud rate [1]
number of signal changes in a second
50
Define the term bandwidth [1]
the range of frequencies that can be transmitted across a network connection
51
Discuss how encrypting data with WPA/WPA2, disabling SSID broadcasting and MAC address whitelisting could enhance the security of a WiFi network [3]
WPA/WPA2 encrypted data reduces chance of unauthorised devices reading transmitted data, SSID broadcast disabled means that SSID wont show up in a search, MAC address whitelisting means only approved devices can join network
52
Explain the process a transmitting device will go through to transmit data using CSMA/CA, RTS/CTS and majority voting [8]
transmitting device checks for traffic, if another transmission in progress transmitter waits, once channel is idle transmitter sends RTS, receiver responds with CTS, if CTS not received, transmitter waits random amount of time before resending RTS, when CTS received transmitter begins transmitting data, receiver sends ACK, if no ACK received then data is resent, majority voting: transmitter would send each bit an odd number of times, receiver checks bits received and if they are not all the same it assumes the one received most is correct
53
Explain an advantage that majority voting has over using parity bits when transmitting data [1]
majority voting can correct errors, can detect multiple errors
54
Describe two differences between machine code and assembly language [2]
machine code is binary but assembly language is written using mnemonics, machine code can be executed without needing to be translated but assembly code needs translating before it is run
55
Describe one similarity and one difference between the role of an assembler and the role of a compiler [2]
both convert source code into object code, assembler takes assembly code as input while compiler takes complex instructions
56
Discuss the ethical and legal issues raised by phone manufacturers to bypass access restrictions on a phone that may contain evidence of criminal activity [9]
breach of privacy, personal data may be lost, law officers may misuse phone, may contact victims, breach of trust between manufacturer and client, may have to let people go free if they cannot access data, breach of human rights of privacy, may be used to solve other crimes, officers may edit data on phone
57
How many different values can be represented using two bytes? [1]
2^16
58
Explain what a check digit is and outline how the check digit is generated [2]
digit is calculated using an algorithm from other digits
59
State Nyquist's theorem [2]
you must sample at a rate that is at least double the highest frequency in the original sound
60
What is a register?
a memory location inside processor
61
Explain why the data bus in a computer system must be bidirectional [2]
when instructions are fetched they have to be transferred from memory to processor, result may need to be transferred back to memory
62
Describe four steps that a processor goes through during the fetch stage of Fetch-Execute [8]
contents of PC transferred to MAR so that PC can be updated, contents of MAR places onto address bus so the correct location in the main memory will be accessed, contents of addressed memory location received on data bus loaded into MBR so that it can cope with the speed difference between the processor and main memory, PC is incremented so that next instruction in sequence can be fetched, contents of MBR copied to CIR so that if data is written execute it does not overwrite the instruction
63
What is immediate addressing? [1]
the operand is the datum
64
Explain why, under the correct conditions, the Vernam cipher is perfectly secure [1]
frequency analysis cannot provide clues to the plaintext
65
Discuss moral, ethical, legal, cultural issues that may arise from using a life blogging device that records audio and video, the data is collected on a server accessed by a website and not telling residents about it [9]
unethical to collect data about people without them knowing what it is used for, unethical to have them wear something without them knowing what it does, observers may watch streams for reasons other than monitoring, invasion of privacy, will data be stored securely, who can see data, data protection regulations, who is responsible for device, how long will data be stored
66
Explain two reasons why an SSD is a better choice for storing and uploading data to a server than a magnetic hard disk [4]
SSDs have lower power drain, faster access time, produce less heat
67
State one reason why a user might choose to compress an image file [1]
takes up less storage space
68
Describe one advantage of lossless over lossy compression [1]
file can be reproduced exactly as it was originally, original data can be fully recovered,
69
Explain how data can be compressed using dictionary-based compression [3]
length strings of symbols of original data are represented by single tokens, a table is formed using the tokens as the key, the strings of symbols are used as the entries
70
Explain the operation of a logical bus network topology [3]
a node broadcasts data, all nodes on network can read the data, only one node can transmit data at a time
71
Explain how it is possible for the bit rate of a comms channel to be higher than its baud rate [1]
bit rate can be higher than baud rate if more than one bit is encoded in each signal change
72
Explain how the receiver will perform error detection on a received bit through even parity [2]
if the number of 1s received is even, the data is assumed to have been received correctly, if the number of 1s received is odd the data has been corrupted
73
State two advantages of serial data transmission and how these are achieved [4]
serial is cheaper as needs fewer wires, does not suffer from crosstalk as only one transmission line, does not suffer from data skewing as only bit transmitted at a time, can be used over long distances as less wires/only one bit at a time
74
During the decode and execute stages of the F-E cycle the instruction is stored in CIR. Explain why the instruction could not be processed directly from the MBR [2]
to execute the instruction other data may need to be fetched, further memory fetches would overwrite the contents of the MBR
75
Explain why the Harvard architecture is sometimes used in preference to the von Neumann architecture [2]
instruction and data can be accessed simultaneously, avoids possibility of data being executed as code
76
State two conditions that must be met for the Vernam cipher to offer perfect security [2]
key must be at least as long as plaintext, key must not be reused, key must be truly random, key must be kept securely
77
Explain the difference between a symmetric and an asymmetric cipher system [1]
symmetric: same key is used to encrypt and decrypt, asymmetric: different keys for encryption and decryption
78
If each voltage level encodes the value of one group of bits, how many bits can be in a group that is encoded by a voltage level, given that eight different voltage levels are used?
3 (2^3= 8)
79
Explain why serial communication is more appropriate than parallel communication [2]
data skew may occur if parallel used, as the longer the distance the higher the likelihood of data skew
80
Explain the general purpose of a D-type flip-flop [1]
used as a memory
81
One input to a D-type flip-flop is a data signal. State what the other input is and what it is used for [2]
clock so state of data input is stored, or to synchronise operation of a group of flip-flops
82
State the purpose of the operand part of an instruction and explain how the addressing mode is related to this [2]
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
83
Discuss the advantages and disadvantages of programming using a high-level language compared to assembly language [4]
program code is easier to understand, faster development time, programs are more portable, assembly language code may execute more quickly, uses less memory, gives direct access to computer hardware
84
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.
* what legal and ethical issues might have arisen as a result of collecting
this data.
* what lessons the company might have learnt from the incident and how
their practices might have changed as a result of it. [12]
how: WiFi signal can travel outside of property, any receiver can read the data packets, a protocol that does not encrypt the transmissions may have been used, to prevent: use a protocol that encrypts data transmissions, limit power of transmitter so does not travel outside, use cabled network, legal: data protection act, computer misuse act, company financially liable for collecting data, different countries have different legislations, what if company had discovered illegal activity, lessons: need for scrutiny of code, need to review guidelines, improved training
85
Explain why a sample rate of 20 000 Hz is not high enough for a faithful reproduction of a sound with a highest frequency of 14 500Hz [2]
Nyquist's theorem states that the sample rate must be at least twice the frequency of the highest frequency in the original signal, 20000 is less than double of 14500, the sample rate should be at least 29000
86
Explain how MIDI represents music and the advantages of using MIDI for representing music instead of using sampled sound [4]
music represented as sequence of MIDI message, usually two or three bytes long, first byte is a status byte, more compact representation, easy to modify, no data lost through sampling
87
Explain the differences between client-server and peer-to-peer networking [4]
client-server: resources stored on server, clients access resources from servers, centralised security, more complex to set up, p2p: resources stored on each individual device, any device can access resources from any other, each device has equal status, management of security is more difficult, no dependence on server
88
Describe how a vector graphic is represented [3]
image is represented as objects, objects have properties which are stored, things such as fill colour, outline colour, width, height of shape are stored
89
Explain why run length encoding is not able to compress an image (with many colours and details) [2]
runs will be of shorter length, the additional run length may cancel out the reduction in storage of pixel colour data
90
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 [12]
hardware: replace processor with one which has more cores, more cache memory, faster clock speed, processor with bigger word size, more RAM, network: replace network cable with one with higher bandwidth, replace wireless connection with wired, use star topology, more efficient protocol, database: use functional programming language, ensure software is compiled, non-relational database system
91
Explain the purpose of the DHCP system, why the DHCP system is used, what will happen during the communication [4]
to automate the configuration of hosts connecting to a network, reduce the need for expert knowledge when configuring a host, host sends request to discover a server, server offers configuration from server
92
The web server, which has the IP address 192.168.16.12, must be accessible from
computers that are connected to the Internet but outside the company’s own network.
As the web server has a non-routable IP address, it cannot be accessed directly from
outside the network. Therefore, access to the web server will be facilitated by the
External Router, which supports Network Address Translation (NAT) and port
forwarding.
Explain how the External Router will have been configured so that the web server can
be accessed by computers outside the network. [2]
93
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 [6]
94
USB Flash Drives (type of SSD) are more popular for transferring files than CD-Rs (optical disk) [1]
95
State two reasons why database designs are usually normalised [2]
96
Explain some of the challenges that face legislators in the digital age [3]
97
Describe two security measures that should be put in place to ensure that the wireless access point (WAP) is secure and explain how these security measures will make wireless connections to the access point more secure [2]
98
One character of a data set that will classify it as Big Data is it containing a variety of different forms of info. Describe two more characteristics of Big Data [2]
99
Describe two different types of resource management that an operating system is responsible for [2]
100
(0 2 . 1 A company is setting up a computer network to help manage its business.
The company sets up a computer that will act as a server. The server’s primary role
will be to act as an email server. It will also allow technicians to remotely login so that
the server can be managed from other computers.)
State the names of two application layer protocols that a server must implement and explain what each will be used for [4]
101
Explain how the transport layer of the TCP/IP stack determines which application layer software on the server should deal with a received request [1]
102
Describe one function of the network layer of the TCP/IP stack [1]
103
Explain how a paragraph of text could be compressed using dictionary-based method [2]
104
Explain why dictionary-based compression is not very effective for small amounts of text [1]
105
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. [12]
106
4 The database is stored at the practice’s head office. Staff at the individual surgeries
access it using a client-server database system, which enables the management of
concurrent access to the database.
Describe an example of a problem that could occur if no system were in place to
manage concurrent access to the database. [3]
107
Two methods that can be used to manage concurrent access are:
* record locks
* timestamp ordering.
Select one of these methods and describe how it manages concurrent access [2]
108
Explain the difference between asynchronous and synchronous communication [1]
109
How is using majority voting instead of parity bit and Unicode instead of ASCII an improvement? Discuss any disadvantages that will result from them. [4]
110
How does a wider data bus speed up the execution of programs [1]
111
Discuss the advantages and disadvantages of representing an image as a vector graphic instead of as a bitmap. Include an example of when to use each [6]
112
Explain what it means for a cipher to be described as computationally secure [1]
113
Explain what the key exchange problem is, in relation to a symmetric cipher [2]
114
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.
You do not need to explain how computer A will encrypt the message or create the
digital signature [4]
115
State one advantage of using a floating point system over fixed and one advantage of fixed over floating [2]
116
How many kibibytes is 4 gibibytes equivalent to?
117
Describe the role of interrupts during the Fetch-Execute cycle [2]
118
Explain the volatile environment (contents of registers) must be saved before an interrupt is serviced [2]
119
Explain the relationship between hardware and software [1]
120
State two reasons why it could be argued that JSON is better than XML [2]
121
State one advantage of using the DHCP system [1]
122
Explain how two or more computers connected to the Internet can have the same IP address and still communicate with each other [2]
123
Explain four different ways that a firewall can protect computers on a LAN [4]
124
A packet of data is to be transmitted across the Internet from Computer A in the UK
to Computer B in Belgium. A checksum will be used to attempt to detect if any errors
have occurred during the transmission.
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. [12]
125
Explain why warehouse owners might prefer the individual products to be identified using RFID tags [2]
126
Explain why product manufacturers or supermarket owners might prefer the individual products to be identified using barcode labels [2]
127
A company provides a box social media service through which members can share
information about themselves and view information and news from their friends.
The service also displays current affairs news stories to its members. The service
does not have journalists who write the stories but instead it uses algorithms to select
news stories written by other organisations and individuals and shows these.
Different news stories may be shown to different members.
Discuss:
* how algorithms might determine which current affairs news stories to display to an
individual member
* the moral, ethical and legal considerations that the developers of the system and its
operators should consider in relation to how the algorithms work and which news
stories are displayed. [6]
128
Explain what a higher-order function is [2]
129
Why do vector graphics take up less storage space than bitmap representations? [3]
130
Describe what thin-client computing is and explain two reasons why a thin-client system might be preferred to a thick-client system [3]
131
If a comms system transmits 4 different signals, with each signal representing two bits of data, describe the relationship between the bit rate and baud rate [1]
132
Explain why a laser printer with a built-in wireless network adapter is likely to be a suitable choice for a printer for a small office [3]
133
Big D box ata is an important application area for modern computer science.
* Describe what Big Data is, using examples to illustrate your description.
* Explain some of the challenges that Big Data brings with it and the approaches that
can be taken to overcome these, in relation to programming and hardware.
* Consider some of the ethical and legal issues that might arise in applications that
store data, particularly data about people. [12]
134
Explain why the relative error is more important than the absolute error [1]
135
Describe what utilities are and given an example of one [2]
136
Describe the role of the control unit [3]
137
One method that can be used to improve the performance of a processor is to
increase the amount of cache memory.
Describe:
* what cache memory is
* what cache memory is used for
* how increasing the amount of cache memory can improve the performance of a
processor. [4]
