OCR GCE Computer Science H446/01: Computer systems A Level Mark Scheme for June 2022

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OCR GCE Computer Science H446/01: Computer systems A Level Mark Scheme for June 2022   OCR GCE Computer Science H446/01: Computer systems A Level Mark Scheme for June 2022 ... OCR (Oxford Cambridge and RSA) is a leading UK awarding body, providing a wide range of qualifications to meet the needs of candidates of all ages and abilities. OCR qualifications include AS/A Levels, Diplomas, GCSEs, Cambridge Nationals, Cambridge Technicals, Functional Skills, Key Skills, Entry Level qualifications, NVQs and vocational qualifications in areas such as IT, business, languages, teaching/training, administration and secretarial skills. It is also responsible for developing new specifications to meet national requirements and the needs of students and teachers. OCR is a not-for-profit organisation; any surplus made is invested back into the establishment to help towards the development of qualifications and support, which keep pace with the changing needs of today’s society. This mark scheme is published as an aid to teachers and students, to indicate the requirements of the examination. It shows the basis on which marks were awarded by examiners. It does not indicate the details of the discussions which took place at an examiners’ meeting before marking commenced. All examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes should be read in conjunction with the published question papers and the report on the examination. © OCR 2022 MARKING INSTRUCTIONS PREPARATION FOR MARKING SCORIS 1. Make sure that you have accessed and completed the relevant training packages for on-screen marking: RM assessor Online Training; OCR Essential Guide to Marking. 2. Make sure that you have read and understood the mark scheme and the question paper for this unit. These are posted on the RM Cambridge Assessment Support Portal http://www.rm.com/support/ca 3. Log-in to RM Assessor and mark the required number of practice responses (“scripts”) and the number of required standardisation responses. YOU MUST MARK 5 PRACTICE AND 10 STANDARDISATION RESPONSES BEFORE YOU CAN BE APPROVED TO MARK LIVE SCRIPTS. MARKING 1. Mark strictly to the mark scheme. 2. Marks awarded must relate directly to the marking criteria. 3. The schedule of dates is very important. It is essential that you meet the 50% and 100% deadlines. If you experience problems, you must contact your Team Leader (Supervisor) without delay. 1. If you are in any doubt about applying the mark scheme, consult your Team Leader by telephone or the RM messaging system, or by email. 2. Crossed Out Responses Where a candidate has crossed out a response and provided a clear alternative then the crossed out response is not marked. Where no alternative response has been provided, examiners may give candidates the benefit of the doubt and mark the crossed out response where legible. Rubric Error Responses – Optional Questions Where candidates have a choice of question across a whole paper or a whole section and have provided more answers than required, then all responses are marked and the highest mark allowable within the rubric is given. Enter a mark for each question answered into RM assessor, which will select the highest mark from those awarded. (The underlying assumption is that the candidate has penalised themselves by attempting more questions than necessary in the time allowed.) Contradictory Responses When a candidate provides contradictory responses, then no mark should be awarded, even if one of the answers is correct. Short Answer Questions (requiring only a list by way of a response, usually worth only one mark per response) Where candidates are required to provide a set number of short answer responses then only the set number of responses should be marked. The response space should be marked from left to right on each line and then line by line until the required number of responses have been considered. The remaining responses should not then be marked. Examiners will have to apply judgement as to whether a ‘second response’ on a line is a development of the ‘first response’, rather than a separate, discrete response. (The underlying assumption is that the candidate is attempting to hedge their bets and therefore getting undue benefit rather than engaging with the question and giving the most relevant/correct responses.) Short Answer Questions (requiring a more developed response, worth two or more marks) If the candidates are required to provide a description of, say, three items or factors and four items or factors are provided, then mark on a similar basis – that is downwards (as it is unlikely in this situation that a candidate will provide more than one response in each section of the response space.) Longer Answer Questions (requiring a developed response) Where candidates have provided two (or more) responses to a medium or high tariff question which only required a single (developed) response and not crossed out the first response, then only the first response should be marked. Examiners will need to apply professional judgement as to whether the second (or a subsequent) response is a ‘new start’ or simply a poorly expressed continuation of the first response. 3. Always check the pages (and additional objects if present) at the end of the response in case any answers have been continued there. If the candidate has continued an answer there then add a tick to confirm that the work has been seen. 7. Award No Response (NR) if: • there is nothing written in the answer space Award Zero ‘0’ if: • anything is written in the answer space and is not worthy of credit (this includes text and symbols). Team Leaders must confirm the correct use of the NR button with their markers before live marking commences and should check this when reviewing scripts. 8. The RM comments box is used by your team leader to explain the marking of the practice responses. Please refer to these comments when checking your practice responses. Do not use the comments box for any other reason. If you have any questions or comments for your team leader, use the phone, the RM messaging system, or e-mail. 9. Assistant Examiners will send a brief report on the performance of candidates to their Team Leader (Supervisor) via email by the end of the marking period. The report should contain notes on particular strengths displayed as well as common errors or weaknesses. Constructive criticism of the question paper/mark scheme is also appreciated. 10. For answers marked by levels of response: a. To determine the level – start at the highest level and work down until you reach the level that matches the answer b. To determine the mark within the level, consider the following: Descriptor Award mark On the borderline of this level and the one below At bottom of level Just enough achievement on balance for this level Above bottom and either below middle or at middle of level (depending on number of marks available) Meets the criteria but with some slight inconsistency Above middle and either below top of level or at middle of level (depending on number of marks available) Consistently meets the criteria for this level At top of level Annotation Meaning Omission mark Benefit of the doubt Subordinate clause / consequential error Incorrect point Expansion of a point Follow through Not answered question No benefit of doubt given Point being made Repeat Correct point Too vague Zero (big) Blank Page – this annotation must be used on all blank pages within an answer booklet (structured or unstructured) and on each page of an additional object where there is no candidate response. Level 1 Level 2 Level 3 11. 12. Subject Specific Marking Instructions Question Answer Mark Guidance 1 (a) (i) ● Both data and instructions share the same memory ● Instructions and Data stored in same format ● A single set of buses / same bus for instructions & data (to connect CPU to Memory and I/O) ● Has a (single) control unit ● Has an ALU. ● Has ways to input and output. ● Has access to storage, ● Works sequentially through instructions // follows Fetch-execute cycle ● (Special) registers within CPU ● Based on stored program concept 2 (ii) ● Separate memory for data and instructions / Multiple memory units ● Different (sets of) buses one for instructions & one for data/ instructions and data can be accessed concurrently. 1 (b) ● Higher/faster clock speed ● More cores//dual/quad/etc core ● More cache memory. 2 Answers must refer to an improvement (more/higher/faster) not just “change the clock speed” Allow discussions of level 1/level 2 cache sizes for one mark. Accept valid features of CPUs that would improve performance e.g. Use of: Pipelining Simultaneous Multithreading Do not accept RISC/CISC. (c) (i) ● 10 ● 60 ● 200 3 1 mark per number (ii) ● Loads a value into the accumulator ● Establishes a zero value (by use of DAT / SUB) ● Stores a zero value into total ● Program stops 4 Example 1 LDA zero STA total HLT zero DAT 0 Example 2 LDA total SUB total STA total HLT BP1 can be given for any value being loaded into the accumulator e.g. INP If candidate writes LDA donation/total (case sensitive) they can get BP2 as they’ve used the labels from the question BP3 - total is case sensitive as given in the question BP4 - must not be given if the zero value will be attempted to be fetched e.g. HLT is placed after DAT (iii) ● One instruction can be fetched while another is being decoded… ● …and another is executed ● The output of one process/instruction is the input of the next. ● Concurrent processing of multiple instructions // completing multiple FDE cycles at once 3 For BP1, allow any 2 of the 3 parts of the FDE cycle For BP2, must give the other part of the FDE cycle not given in BP1 Do not award if explaining multiple cores working on different parts of FDE cycle (iv) ● More instructions can be carried out in a set amount of time // less time to execute the same number of instructions ● Increasing the speed/performance/efficiency of the computer/program // quicker for the program to complete 2 Do not allow “each instruction is quicker to execute”. BP2 has to be specific to the charity e.g. processing more donations (d) (i) ● Holds all input/output ● Holds results of calculations (from the ALU) ● Checked for conditional branching (e.g. BRZ) ● Stores data which has come from the MDR/RAM 2 (ii) ● Holds the address/location of the next instruction (to be executed/fetched) ● Contents copied to the MAR at start of FDE ● Incremented (by one) on every cycle ● Can be changed by branch/jump instructions 2 (iii) ● Memory Address Register // MAR ● Memory Data Register // MDR ● Current Instruction Register // CIR ● Index Register // IR 3 Allow Memory Buffer Register for MDR (e) Mark Band 3–High Level (9-12 marks) The candidate demonstrates a thorough knowledge and understanding of both CISC and RISC. The material is generally accurate and detailed. The candidate is able to apply their knowledge and understanding directly and consistently to the context provided. Evidence/examples will be explicitly relevant to the explanation. The candidate provides a thorough discussion which is well balanced. Evaluative comments are consistently relevant and well-considered. There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated. Mark Band 2-Mid Level (5-8 marks) The candidate demonstrates reasonable knowledge and understanding of CISC and/or RISC; the material is generally accurate but at times underdeveloped. The candidate is able to apply their knowledge and understanding directly to the context provided although one or two opportunities are missed. Evidence/examples are for the most part implicitly relevant to the explanation. The candidate provides a sound discussion, the majority of which is focused. Evaluative comments are for the most part appropriate, although one or two opportunities for development are missed. There is a line of reasoning presented with some structure. The information presented is in the most part relevant and supported by some evidence. 12 AO1.1 (2), AO1.2 (2), AO2.1 (3), AO3.3. (5) AO1 CISC is a complex instruction set. The traditional approach to processor design. Lots of instructions available although some instructions in CISC will rarely get used. RISC is a reduced instruction set. A smaller number of instructions available, several instructions can be combined to perform the same tasks as CISC processors. RISC instructions are used regularly. RISC has fewer transistors/less complex circuitry whereas CISC integrated circuits are more expensive/complicated. RISC instructions take one cycle whereas CISC may take several. RISC can only do complex things by combining multiple instructions whereas CISC is done in one line. Compilers for RISC need to be more complex than compilers for CISC AO2 CISC processors would run the same software as the desktop machines. Would be less power efficient and require larger battery and cooling mechanisms. More expensive to purchase. RISC processor requires software to be written specifically for it (cannot use CISC instructions). More power efficient and so requires less/no cooling and smaller battery/longer battery life. RISC devices may require greater RAM as programs tend to be larger than their CISC equivalents. AO3 Mobile use of CISC would save money on software and increase compatibility but cost more to purchase and be physically larger (heat sink/larger battery) and/or have a shorter battery life. RISC would require investment in software but be cheaper to purchase and give a better performance out Mark Band 1-Low Level (1-4 marks) The candidate demonstrates a basic knowledge of CISC or RISC; the material is basic and contains some inaccuracies. The candidate makes a limited attempt to apply acquired knowledge and understanding to the context provided. The candidate provides a limited discussion which is narrow in focus. Judgments if made are weak and unsubstantiated. The information is basic and communicated in an unstructured way. The information is supported by limited evidence and the relationship to the evidence may not be clear. 0 marks No attempt to answer the question or response is not worthy of credit. of the office (lighter/longer battery life). Some compatibility issues may be reduced with emulators and translators. [Show More]

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