A-Level Computer Science Exam Questions

3. Below is an algorithm that draws a triangle. Algorithm i is integer j is integer k is integer n is integer input n for i = 0 to n set j = n while j > i output ‶ ″ set j = j - 1 end while set k = n while k >= n - i output ‶I″ set k = k - 1 end while next i (a) Evaluate the efficiency of the algorithm and, using Big O notation, determine the growth rate for the time performance. [5] (b) Draw a graph of the algorithm above to illustrate its order of time efficiency. Graph paper is not required. [4] (c) Determine the growth rate of memory use during a single run of the algorithm. [2] Turn over 3 A500U101 03 (A500U10-1) © WJEC CBAC Ltd.

4. Below is an algorithm. (a) Describe the lifetime of variable m in the function straightLine. [2] (b) Describe the scope of variable y. [2] 5. Explain how current computer security legislation protects businesses, individual users and national security. [8] 4 © WJEC CBAC Ltd. (A500U10-1)

6. Describe the purpose of the following mathematical operations in algorithms. (a) DIV [2] (b) MOD [2] (c) Below is an algorithm that makes use of the MOD operator. (i) Explain the purpose of the algorithm. [2] (ii) Explain the use of sequence in the algorithm. [2] (iii) Explain the use of selection in the algorithm. [2] Turn over 5 © WJEC CBAC Ltd. (A500U10-1)

7. A festival ticket supplier produces a unique ticket validation code with each ticket purchase. This validation code comprises four parts: the buyer's surname, the digits from their postcode, an ID and a randomly generated hexadecimal value. Each part is separated with chevrons (»). • The surname can only contain uppercase letters. • The postcode can only contain digits. • The ID must contain 6 digits. • The hexadecimal value uses digits and / or uppercase letters and can be of any length. • Chevrons (»). Example: ZAKS»63»300700»4BAF76C2D7 Produce a Backus-Naur Form (BNF) definition for the validation code. [6] 8. Explain the use of program version management in software engineering. [8] 9. A local shop has approached a software company to build a web application with the following requirements: • To display all the products they have in store through a modern user interface (UI). • To allow customers to find and filter products through the web application. • To allow staff to login and create, edit, delete and view products through a back-end database. Explain why it will be important to analyse these requirements using decomposition and abstraction. [6] 10. Write a Bubble Sort algorithm in pseudo-code that will sort the contents of a one-dimensional integer array (myArray) into descending order. [9] 11. Explain the ambiguities in natural language syntax compared with computer language syntax. [8] 12. Discuss the importance of promoting professional behaviour given the social changes that have occurred as a result of developments in computing and computer use. You should draw on your knowledge, skills and understanding from a number of areas across your computer science course when answering this question. [12] END OF PAPER 6 © WJEC CBAC Ltd. (A500U10-1)

2 4. In the examination room before the examination starts i. When told to do so by the invigilator, log onto your workstation and follow the instructions below to decrypt the media files using 7-Zip. ii. Access your user area on your workstation. Your user area will contain a file with a .7z suffix like this one: iii. Right click this file, choose 7-Zip and then Open archive as shown below. 3 iv. You will then be asked for the password (this will be case sensitive). You can find this on the first page of these instructions. Type in this password in the box provided. This may be easier if you tick the Show password box as below. Click OK when you’ve entered the password. v. In the next window choose extract. 4 vi. Just click OK at the next window. vii. The program will then extract all the files you need, and you are ready to start the examination when told to do so by the invigilator.

5 5. In the examination room after the examination has finished. You will need to zip all your files following the instructions below: i. Highlight all the files in your folder either by pressing Ctrl A or by using the mouse. ii. Right click and choose 7-Zip then Add to archive. 1 Example files only 6 iii. Fill out the archive name with your candidate number followed by your surname and initials. DO NOT ENTER ANY ENCRYPTION DETAILS. IF YOU DO YOU MAY NOT RECEIVE MARKS FOR YOUR WORK iv. Then click OK. 6. Leaving the examination room after the examination has finished. You have now finished and can leave the examination room when told to do so by the invigilation staff.

(A500U10-1) 5 12. Discuss the possible effects of computers on the nature of employment in the computing industry and wider society. You should draw on your knowledge, skills and understanding from a number of areas across your computer science course when answering this question. [12] END OF PAPER © WJEC CBAC Ltd. BLANK PAGE (A500U10-1) 6 © WJEC CBAC Ltd. BLANK PAGE (A500U10-1) 7 © WJEC CBAC Ltd.

(A500U20-1) 7 11. The transfer speeds between the nodes of a network have the values shown in this diagram. A B C H G F E D 100 Kbps 100 Kbps 50 Kbps 100 Kbps 50 Kbps 50 Kbps 50 Kbps 250 Kbps 250 Kbps 250 Kbps 40 Kbps 50 Kbps 100 Kbps 200 Kbps 200 Kbps The cost for routing data between nodes is calculated by dividing 1Mbps by the transfer speed of the link. For example: Cost for the link A to B = = = 4 Data are transmitted between source and destination by the route which has the lowest total cost. (a) Copy the table below into your answer booklet. Complete the table to show the cost and transmission route that would be taken from source to destination. [4] Source Destination Cost Route A F E G (b) Calculate, to the nearest second and showing all of your working, the time required to transfer 220 KB (Kilo Bytes) of data from node G to node H. [4] 12. Partitioning of main memory is a responsibility of the operating system’s memory management function. Explain the need for partitioning of main memory, the different methods that can be used for partitioning and possible consequences associated with these methods. [9] END OF PAPER © WJEC CBAC Ltd. 1Mbps 250Kbps 1000 000 250 000

Turn over. (2500U20-1) 5 © WJEC CBAC Ltd. 1 start is integer 2 . . . 3 . . . 4 mid is integer 5 6 set start = 0 7 set endv = 9999 8 . . . 9 10 input searchValue 11 12 repeat 13 set mid = (start + endv) DIV 2 14 . . . 15 set found = TRUE 16 output “SearchValue found at position”, Mid 17 endif 18 19 . . . 20 . . . 21 endif 22 23 if searchValue < stockCost[mid] then 24 set endv = mid – 1 25 endif 26 . . . 27 28 . . . 29 output “searchValue not found” 30 endif 31 End (b) This is an algorithm for a binary search. Fred’s intends to use the binary search algorithm shown to search the array stockCost. Several lines are missing from the algorithm. Copy the algorithm into your Section A answer document and complete it using lines selected from this list; [8] • endv is integer • set start = mid + 1 • if found = FALSE • found is Boolean • set found = FALSE • if searchValue = stockCost[mid] then • until (found = TRUE) OR (endv < start) • if searchValue > stockCost[mid] then (2500U20-1) 6 Section B: Develop programs Select the programming language of your choice from section BI, BII or BIII and answer both questions within your chosen section. BI Visual Basic Fred’s wants a prototype computer system to be developed using Visual Basic. 1. Open the file stock • Read through the code and familiarise yourself with its contents. • The file contains incomplete code which attempts to save stock details and return the number of stock items on file that match the search criteria entered e.g. expiry date. Complete this code. Save the changes made to the file stock. [8] 2. Using the internal facility of your chosen language, annotate the code from Question B1 above to clearly explain the design of this program to another software developer. Save the changes made to the file stock. [8] © WJEC CBAC Ltd. (2500U20-1) 7 © WJEC CBAC Ltd. Turn over. BII Java Fred’s wants a prototype computer system to be developed using Java. 1. Open the file stock • Read through the code and familiarise yourself with its contents. • The file contains incomplete code which attempts to save stock details and return the number of stock items on file that match the search criteria entered e.g. expiry date. Complete this code. Save the changes made to the file stock. [8] 2. Using the internal facility of your chosen language, annotate the code from Question B1 above to clearly explain the design of this program to another software developer. Save the changes made to the file stock. [8] (2500U20-1) 8 © WJEC CBAC Ltd. BIII Python Fred’s wants a prototype computer system to be developed using Python. 1. Open the file stock • Read through the code and familiarise yourself with its contents. • The file contains incomplete code which attempts to save stock details and return the number of stock items on file that match the search criteria entered e.g. expiry date. Complete this code. Save the changes made to the file stock. [8] 2. Using the internal facility of your chosen language, annotate the code from Question B1 above to clearly explain the design of this program to another software developer. Save the changes made to the file stock. [8] END OF PAPER

(1500U30-1) 5 11. This algorithm duplicates a three-dimensional array of length n. You can assume the array (myArray) has already been populated with data. © WJEC CBAC Ltd. (a) Evaluate the efficiency of the algorithm and using Big O notation, determine the growth rate for time performance. [5] (b) Determine the growth rate of memory space during a single run of the algorithm. [2] (c) Identify the type of time complexity and draw a graph of the algorithm to illustrate the order of time performance. Graph paper is not required. [2] 12. Describe how data may be recovered if lost. [4] 13. Discuss the importance of codes of conduct in promoting professional behaviour throughout the software development stages. You should draw on your knowledge, skills and understanding from a number of areas across your computer science course when answering this question. [12] END OF PAPER 1 declare i,j,k,n as integer 2 declare myArray[n,n,n] 3 declare myArrayCopy[n,n,n] 4 5 set i = 0 6 set j = 0 7 set k = 0 8 9 for i = 0 to n - 1 10 11 for j = 0 to n - 1 12 13 for k = 0 to n - 1 14 15 set myArrayCopy[i,j,k] = myArray[i,j,k] 16 17 next k 18 19 next j 20 21 next i BLANK PAGE 6 © WJEC CBAC Ltd. (1500U30-1) © WJEC CBAC Ltd. BLANK PAGE (1500U30-1) 7 © WJEC CBAC Ltd.

6 (1500U40-1) © WJEC CBAC Ltd. 10. (a) Describe what is meant by the term relational database. [2] (b) Describe the advantages of database normalisation. [4] A health care company is creating a relational database to manage its dental surgeries located in different towns across Wales. Each dental surgery employs dentists who will only work in that surgery. Patients will be registered with one of the dentists and will only be treated by that dentist. Patients will book appointments to see their dentist. (c) Produce an entity relationship diagram for the system described. [3] (d) Design a database structure in third normal form for the system. [3] 11. The increase in speed due to parallel processing can be calculated as: where P = parallel fraction, N = number of processors and S = serial fraction. (S = 1 – P) (a) Calculate the increase in speed due to parallel processing using 10 processors and the increase in speed of doing the same task using 1000 processors, where the parallel fraction P is equal to: • 0.5 for 10 and 1000 processors • 0.9 for 10 and 1000 processors [4] (b) Discuss the effect that increasing the parallel fraction of the task will have on the speed due to parallel processing. [3] 12. Describe the advantages of using a distributed database. [4] 13. Cryptography may be based on symmetric or asymmetric algorithms. Describe the advantages of using asymmetric encryption. [6] 14. A local hospital needs to ensure that access to its medical laboratories is restricted to authorised personnel. It is considering using biometric technologies to identify and restrict access to authorised personnel only. Describe the biometric options available to the hospital and explain the main benefits and drawbacks of biometric security technologies. [9] END OF PAPER 1 P s + N S BLANK PAGE (1500U40-1) 7 © WJEC CBAC Ltd.

16 (2500U10-1) Examiner only 13. Describe, giving an example, one type of maintenance performed on a computer program. [3] © WJEC CBAC Ltd. (2500U10-1) Turn over. 17 Examiner only 14. Andrew is considering using three different methods for storing positive numbers, using two’s complementation, in a computer system. © WJEC CBAC Ltd. METHOD 1 Store numbers as an integer using an 8 bit register. METHOD 2 Store real numbers in normalised floating-point form, using a 5 bit mantissa and a 3 bit exponent. METHOD 3 Store real numbers in normalised floating-point form, using a 4 bit mantissa and a 4 bit exponent. Calculate the denary range (highest and lowest) of numbers that can be stored by each method. Compare the advantages of representing numbers in integer and floating-point forms. [12] 18 (2500U10-1) Examiner only END OF PAPER © WJEC CBAC Ltd. (2500U10-1) Turn over. 19 © WJEC CBAC Ltd. For continuation only. Examiner only (2500U10-1) 20 © WJEC CBAC Ltd. For continuation only. Examiner only

2 4. In the examination room before the examination starts i. When told to do so by the invigilator, log onto your workstation and follow the instructions below to decrypt the media files using 7-Zip. ii. Access your user area on your workstation. Your user area will contain a file with a .7z suffix like this one: iii. Right click this file, choose 7-Zip and then Open archive as shown below. 3 iv. You will then be asked for the password (this will be case sensitive). You can find this on the first page of these instructions. Type in this password in the box provided. This may be easier if you tick the Show password box as below. Click OK when you’ve entered the password. v. In the next window choose extract. 4 vi. Just click OK at the next window. vii. The program will then extract all the files you need, and you are ready to start the examination when told to do so by the invigilator.

5 5. In the examination room after the examination has finished. You will need to zip all your files following the instructions below: i. Highlight all the files in your folder either by pressing Ctrl A or by using the mouse. ii. Right click and choose 7-Zip then Add to archive. 1 Example files only 6 iii. Fill out the archive name with your candidate number followed by your surname and initials. DO NOT ENTER ANY ENCRYPTION DETAILS. IF YOU DO YOU MAY NOT RECEIVE MARKS FOR YOUR WORK iv. Then click OK. 6. Leaving the examination room after the examination has finished. You have now finished and can leave the examination room when told to do so by the invigilation staff.

(1500U30-1) 5 12. This is an algorithm which searches for consecutive data items in three separate one dimensional arrays all of size n. You can assume all the arrays have already been populated with data. © WJEC CBAC Ltd. (a) Evaluate the efficiency of the algorithm and using Big O notation, determine the growth rate for time performance. [5] (b) Draw a graph of the algorithm to illustrate and identify its order of time performance. Graph paper is not required. [4] 13. Discuss contemporary approaches to human-computer interaction. You should draw on your knowledge, skills and understanding from a number of areas across your computer science course when answering this question. [13] END OF PAPER Algorithm Search declare i as integer declare myArray1[n] as integer[] declare myArray2[n] as integer[] declare myArray3[n] as integer[] declare found as string set i = 0 set found = “” do if myArray1[i] = myArray1[i+1] then set found = found + myArray1[i] + “ “ end if if myArray2[i] = myArray2[i+1] then set found = found + myArray2[i] + “ “ end if if myArray3[i] = myArray3[i+1] then set found = found + myArray3[i] + “ “ end if set i = i + 1 while (i < n) output “Consecutive data items found: “ , found BLANK PAGE 6 © WJEC CBAC Ltd. (1500U30-1) 6 © WJEC CBAC Ltd. BLANK PAGE (1500U30-1) 7 © WJEC CBAC Ltd.

(1500U40-1) Turn over. 5 © WJEC CBAC Ltd. 10. A kitchen equipment shop uses a database to record information about products and orders. Two tables with example records are shown: Product ProductID Description Model Price 108 Cooker Ultrachef 342.80 112 Dishwasher Speedclean 291.50 134 Freezer IceKing 188.80 196 Cooker MasterKitchen 405.60 Order OrderID Customer ProductID OrderDate Delivered 6291 R. Kelling 108 23 Mar 2020 True 7821 G. Hambleton 112 07 Apr 2020 False 9215 P. Yang 108 19 May 2020 False 9851 S. West 196 22 May 2020 True (a) Write an SQL command to list only the description and price for each Product record where the price is less than 300. [2] (b) Write an SQL command to list the customer and order date for all orders with a product description ‘Cooker’. [3] (c) Write an SQL command to add the following record to the Product table: A refrigerator with the model name ‘Coolstore 2000’. This has been allocated Product ID 288 and has a price of 150.60. [2] 11. A large company has many departments, each of which has different responsibilities. When a major project is carried out, employees from the departments need to work together. (a) The company currently uses a single flat file to store all details of the projects. They have discovered that the data structure has several shortcomings. Describe two disadvantages for the company of using a flat file to store its data. [4] (b) The company has decided to develop a relational database to store details of the projects. Each project will have a title and a project budget. Project teams will be made up of employees from various departments. Each time an employee joins the company they will be allocated to the department that matches their skills. An employee may be a member of more than one project team. Design a database system in third normal form for this situation. [5]

6 (1500U40-1) © WJEC CBAC Ltd. 12. (a) Explain what is meant by a distributed system and describe what will be distributed in the system. [2] (b) A car manufacturer has a number of dealerships across the UK. Car owners take their cars for servicing each year to a convenient dealership. Records are kept of servicing, any faults found, and replacement parts fitted. Explain the advantages to the company of implementing a distributed database system across its dealerships compared with using a single centralised database. [4] 13. (a) Explain the advantages and disadvantages of single key (symmetric) encryption compared with double key (asymmetric) encryption, giving an example, for each method, of a situation where that method would be the most suitable. [6] (b) Text is stored in 8-bit binary ASCII format, with numeric codes representing each character: A = 6510 0100 00012 B = 6610 0100 00102 C = 6710 0100 00112 The text is encrypted using a sequential XOR method: • The first character is encrypted by XOR with the key value 0110 10102 • The second character is encrypted by XOR with the encrypted value of the first character • The third character is encrypted by XOR with the encrypted value of the second character Using this algorithm, encrypt the word CAB. [3] 14. (a) Identify two hardware devices required to make a wireless connection to a network. [2] (b) State two protocols used for wireless digital communication. [2] (c) Describe one disadvantage of using a public wireless network. [2] 15. Information and advice on medical and health issues are readily available to the public through the internet, including online expert systems. Discuss the possible effects of using the internet for this purpose on health professionals and the wider community. [9] END OF PAPER (1500U40-1) 7 © WJEC CBAC Ltd. BLANK PAGE