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OCR A Level Computer Science H446/01 Computer systems Comprehensive Solutions + Official MARKING SCHEME Oxford Cambridge and RSA Wednesday 11 June 2025 — Morning A Level Computer Science H446/01 Computer systems Time allowed: 2 hours 30 minutes You can use: * aruler (cm/mm) * an HB pencil Do not use: + acalculator Please write clearly in black ink. Do not write in the barcodes. Centre number Candidate number First name(s) Last name INSTRUCTIONS + Use black ink. You can use an HB pencil, but only for graphs and diagrams. + Write your answer to each question in the space provided. If you need extra space use the lined pages at the end of this booklet. The question numbers must be clearly shown. + Answer all the questions. INFORMATION + The total mark for this paper is 140. The marks for each question are shown in brackets [ ]. Quality of extended response will be assessed in questions marked with an asterisk (*). * This document has 32 pages. ADVICE + Read each question carefully before you start your answer. 3 Charlie is about to study a computer games design course at university. He needs to purchase a computer to allow him to design and edit the graphics in his games, including video files. (a) Charlie’s computer contains a data bus, an address bus and a control bus. State the purpose of each of these three buses. Data DUS oon ceceececeeeceneeecneeeee concen ceeeeesesacea cave ceaesaeaesose cesses essusensnssesessesensasecensensessaseneeceaeeeteteee (b) Charlie will need to use input and output devices when designing and editing his computer games. State one input device and one output device that Charlie could use and give an example use of each. Input device Device name Output device Device name © OCR 2025 Tum over 4 (ii) Charlie will need to store a large collection of files containing high definition images and high definition videos that he will use during his course. State a type of secondary storage device that Charlie could use and give a reason why. Type of storage [2] (c) In addition to the Central Processing Unit (CPU), Charlie will purchase a Graphical Processing Unit (GPU) that will be used to process and display the graphics in his games. (i) Tick (V) one box on each row to indicate if each statement is referring toa CPU or a GPU. Statement CPU GPU Suited to performing simple operations in parallel on larger data sets Suited to performing complex operations on smaller data sets [2] (ii) State two benefits of using a GPU to process and display the graphics in computer games. Berefit 1 nee ee cee ceeceseeeseeeneeceneeeceesensesae ceaeea conse sesaee cesses ecsuseceassasecseee cease seesensnseaseneeeeanenteeeerens Berefit 2 nee cece ces eececeee cece cneseeeceneeecneseeseeaeeceseea conse sesaee cesses ecsueeceassaseseee cease seaseanseesenseeeasenteeeerees [2] (d) Charlie will require an operating system that will allow him to have several applications open at the same time. (i) State which type of operating system Charlie will need to install. oc eessesestosssusstunstonnstosstunesssnstinestunestonstsnstinstonstitestinestinestisestinessestestineestaneeseeeees [1] ©OCR 2025 6 2 OCR Consultants is designing a computer for a large company. (a) OCR Consultants is designing the architecture of the CPU. (i) Compare two differences between the Von Neumann architecture and the Harvard architecture. Difference 1 [4] (ii) OCR Consultants is considering using pipelining. State two benefits of using pipelining. Bernetit 1 ones ceeeeseeecneeeeeceneeecneeeeseeae ceseeaesesacsesaee cease ceseseceaseasessaee cease seasenseseaseneeseasenteeeerens Berefit 2 nee cece ces eececeeeeceeecneseeeceneeeceeeseseene ceaeeaaesacsesase cesses eesueeceussaseseee cease seesensnseaseneeseaeenteseerens [2] ©OCR 2025 7 (iii) OCR Consultants can base the CPU around a RISC architecture or a CISC architecture. Compare two differences between a RISC architecture and a CISC architecture. Difference 1 © OCR 2025 Tum over © OCR 2025 Tum over 10 3 (a) (i) Convert the denary number 189 into an 8-bit binary number. (b) Explain the effect that a right shift of three places will have ona positive binary number. ©OCR 2025 12 (d) (i) Show the result of applying a bitwise AND mask of 1010 1110 to the byte 1010 0011. Byte 1010 0011 AND Mask 1010 1110 Result (ii) State the purpose of the bitwise AND mask. ©OCR 2025 [2] 13 4 Kofi is a software engineer and has been asked to write some code using the Little Man Computer (LMC) instruction set. (a) State the LMC command that would be used for each description given in the table. Description LMC Command Load the value stored in the memory address into the accumulator Branch without checking the value in the accumulator Store the value from the accumulator into a memory address Branch if zero is in the accumulator Branch if zero or a positive number is in the accumulator [3] Kofi has been asked to write a program that inputs two numbers and then outputs the largest of the two numbers. (b} Write the code for this program using the LMC instruction set. You can assume that the two numbers will always be different. © OCR 2025 Tum over 15 © OCR 2025 Tum over 1€ 5 This diagram shows the logic circuit for a half adder. A »——\ C (Out) (a) Complete the truth table for this half adder circuit. A B s C (Out) 0 0 0 1 1 0 1 1 [4] (b) Describe the difference between a half adder circuit and a full adder circuit. ©OCR 2025 
