9608_s15_qp_33
A paper of Computer Science, 9608
Questions:
6
Year:
2015
Paper:
3
Variant:
3
Login to start this paper & get access to powerful tools
1
The following syntax diagrams, for a particular programming language, show the syntax of: • an assignment statement • a variable • a number • a letter • a digit • an operator Variable Assignment statement Variable Digit := Variable Operator Number Letter Number Number Digit Letter A B C Operator + – / The following assignment statements are invalid. Give a reason in each case. A2 = B3 + 123 Reason B3 := B3 – 203 Reason A2414 := A3 * B Reason Complete the Backus-Naur Form (BNF) for the syntax diagrams shown on the opposite page. has been done for you. ::= ::= ::= ::= A | B | C ::= ::= A company develops software. It provides virtual machines for its software developers. The company has a large number of clients who use a wide range of hardware and software. Explain the term virtual machine. Ensure that your answer includes the terms hardware and software. Give one benefit to the company of using virtual machines. Give one drawback to the company of using virtual machines.
3. Advanced Theory  →  3.4. System software
2. Fundamental Problem-solving and Programming Skills  →  2.3. Programming
Open
2
Four descriptions and three types of local area network (LAN) are shown below. Draw a line to connect each description to the type of LAN it applies to. Description Type of LAN Any packet the listening computer receives may be part of a message for itself Bus with terminators at each end Connection provided through an access point Star A process for handling collisions has to be implemented Wireless Listening computer only receives packets that are addressed to itself A user downloads a file using the FTP protocol. Explain the function played by each of the following: Server Command Anonymous
3. Advanced Theory  →  3.2. Communication and Internet technologies
1. Theory Fundamentals  →  1.2. Communication and Internet technologies
Open
3
The incomplete table below shows descriptions and terms relating to malware. Complete the table with appropriate descriptions and terms. Description Term A Sending emails which contain a link to a website that attempts to trick users into giving confidential personal data. B It replicates by inserting itself into another piece of software. C Worm D Spam Choose term A or term B and describe: • a problem that might arise for a user • a possible solution to the problem Term Problem Solution Explain the following terms: Cipher text Private key Bill, a manager of a company, sent an email with very sensitive information to a work colleague, Alison. However, Bill also accidentally sent it to everybody in the company. Describe the method used that ensured only Alison was able to read the original contents of the email.
3. Advanced Theory  →  3.5. Security
Open
4
A particular programming language allows the programmer to define their own data types. An example of a user-defined data type for an address is: TYPE ThisAddress DECLARE ThisHouseNo : INTEGER DECLARE ThisStreet : STRING DECLARE ThisTown : STRING ENDTYPE A variable of this new type is declared as follows: DECLARE HomeAddress : ThisAddress Write the statement that assigns the house number 34 to HomeAddress. The type definition for ThisAddress is to be changed. Rewrite one line from the definition for each of the following changes. House numbers are in the range from 1 to 10. DECLARE The possible towns are limited to: Brightown, Arunde and Shoram. DECLARE Temperature data from a number of weather stations are to be processed by a program. The following data are to be stored: • weather station ID (a unique four-letter code) • latitude (to 2 decimal places) • average temperature (to the nearest whole number) for each year from 2001 to 2015 inclusive A programmer designs a composite data type WeatherStation. A variable of this type can be used to store all the data for one particular station. Write the definition for the user-defined data type WeatherStation. The programmer decides to store all the data in a file. The number of weather stations could grow to reach 20000, but not all stations will be present at first. The programmer decides on random organisation for the file. Describe three steps which show how a new weather station record is added to the file.
3. Advanced Theory  →  3.1. Data representation
4. Further Problem-solving and Programming Skills  →  4.1. Computational thinking and problem-solving
2. Fundamental Problem-solving and Programming Skills  →  2.3. Programming
Open
5
Complete the truth table for this logic circuit: A B X A B Working space X Complete the truth table for this logic circuit: A B X A B Working space X A student decides to write an equation for X to represent the full behaviour of each logic circuit. Write the Boolean expression that will complete the required equation for X for each circuit: Circuit 1: X = Circuit 2: X = Write the De Morgan’s Law which is shown by your answers to part and part . Write the Boolean algebraic expression corresponding to the following logic circuit: A B X Using De Morgan’s laws and Boolean algebra, simplify your answer to part . Show all your working.
3. Advanced Theory  →  3.3. Hardware
Open
6
A company grows vegetables in a number of large greenhouses. For the vegetables to grow well, the temperature, light level and soil moisture need to always be within certain ranges. The company installs a computerised system to keep these three growing conditions within the best ranges. Sensors are used for collecting data about the temperature, light level, and moisture content of the soil. Name the type of system described. Give three items of hardware that would be needed for this system. Justify your choice. Do not include sensors in your answer. Item 1 Justification Item 2 Justification Item 3 Justification Describe what is meant by feedback in the above system. When the system was designed, various parameters for temperature were set. Name one of these parameters. Explain how this parameter value is used by the feedback system. Question 6 continues on page 14. Each greenhouse has eight sensors (numbered 1–8). • The byte at address 150 is used to store eight 1-bit flags. • A flag is set to indicate whether its associated sensor reading is waiting to be processed. • More than one sensor reading may be waiting to be processed at any particular moment. • Data received from the sensors is stored in a block of eight consecutive bytes (addresses 201–208). • The data from sensor 1 is at address 201, the data from sensor 2 is at address 202, and so on. Sensor number Interpret the current reading for sensor 2. The accumulator is loaded with the data from location 150. Write the assembly language instruction to check whether there is a value waiting to be processed for sensor 6. LDD 150 // data loaded from address 150
3. Advanced Theory  →  3.6. Monitoring and control systems
1. Theory Fundamentals  →  1.4. Processor fundamentals
Open