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OCR A Level Computer Science H446/01 Computer systems Exam Questions and CORRECT 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: * a calculator WN - Please write clearly in black ink. Do not write in the barcodes. Centre number Candidate number First name(s) Last name NX 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. © OCR 2025 [601/4911/5] OCRis an exempt Charity Dc (PQICB) 340531/5 Tum over 2 BLANK PAGE DO NOT WRITE ON THIS PAGE ©OCR 2025 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 5 (ii) An operating system that Charlie is thinking about installing uses a multi-level feedback queue. Describe how a multi-level feedback queue works. (iii) An operating system manages and installs device drivers. Explain why hardware devices require a device driver. (e) Once Charlie has installed an operating system he will need to install utility software. State two utilities that Charlie could install and state the purpose of each. Utility Vee eee ec ceeceneeesneenesceneencneeaeaneae cease casa snsane cesses cesneeseassaseteeee cease seasenseseaseneeseatenseeeetens © OCR 2025 Tum over 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 8 (b)* The employees of the large company work remotely from home and use large databases that store a lot of sensitive data. They need to be able to use the databases to search and sort data quickly. OCR Consultants is considering two approaches: + thin client approach — this is where the database is stored virtually on a remote server. All of the data processing is also completed on a remote server on virtual machines. The employees’ computers are only used to capture the data input and display the results from the virtual machines + — thick client approach — this is where most of the processing is done on the employees’ computer using specialised software to access the remote database. Discuss the benefits and drawbacks of each of these approaches. You should include the following in your answer: + what is meant by virtual machines and virtual storage + the benefits and drawbacks of a thin client and thick client approach described in the question * — aconclusion justifying which approach would be most suitable for this scenario. [9] © OCR 2025 Tum over 11 (c) Show the subtraction of these two floating point binary numbers. Both numbers are stored in a normalised floating point format, using 6 bits for the mantissa and 4 for exponent. You should show your result in the same format. Show your working out. 011010 0011 — 010010 0010 WOSKING SPACE oo... eee eee eceeceeeeceeseeceeeeecesesee ceseeeceseseeceueee cess eeseececseeescece cesses ceeseeecaceeceeeeeneeeeseceeecemeeeee Final 6-bit mantissa «0.00.00 Final 4-bit exponent ......... 202.0... eects [6] © OCR 2025 Tum over 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] 14 (c)* Kofi is working on a number of projects. These include: * project 1 — Writing a mobile phone app to look at the news * project 2 — Writing software to send temperature readings from an embedded heat sensor to other devices * project 3— Writing an image editing application for a desktop computer * project 4 — Writing software to calculate the results of a physics experiment that produces terabytes of data * project 5 — Writing a new device driver for a new piece of hardware. Discuss which of these projects should be written in a high level programming language and which should be written in a low level language. You should include the following in your answer: + what is meant by high level programming language and low level language + which projects are suitable for high level and which are suitable for low level languages + aconclusion that justifies why these different languages are needed. [12] 15 © OCR 2025 Tum over 17 (c) The diagram below shows a partially completed logic circuit for a full adder. The full adder circuit contains three inputs: + A-represents the first input + B-represents the second input + C(in)—represents the carry bit from the previous stage of the addition. The full adder circuit contains two outputs: + Sum -represents the result of adding the three inputs A, B and C(in) + C(out)— represents the carry that is passed to the next stage of the addition. Complete the logic circuit to represent a full adder. A @Sum B-@—_@e—_ C(in) -@ @ C(out) [4] © OCR 2025 Tum over 18 (d) This Karnaugh map represents a different logic circuit. AB 00 01 11 10 00 0 1 1 1 01 cD 0 1 1 0 11 0 0 0 0 10 0 0 1 1 Use this Karnaugh map to find the simplified expression for this circuit. You should annotate the Karnaugh map to show the groups that you have used to find the simplified expression. Write your simplified expression here. ©OCR 2025 
