OCR GCSE Computer Science (J277/2020) Past Papers 2026

Computer Systems

Duration: 1h 30m

Computational Thinking, Algorithms and Programming

Duration: 1h 30m

Logic errors in programs — identifying and correcting off-by-one errors and incorrect compound conditions

J277/02 Q2(b) June 2023 and Q3(b) June 2024: in 2023 'far fewer [candidates] were able to successfully fix the errors satisfactorily' despite many finding the first error. In 2024 the correction to a multi-condition line (requiring two separate comparisons with the variable named on each side of AND) was 'commonly done incorrectly'. The specific misconception that 'if total >= 10 and <= 20' is valid syntax was highlighted in a dedicated Misconception box.

J277/02

Function parameters — re-inputting values that are already passed as parameters

J277/02 Q8(b) June 2024: the question provided two parameters (direction and position) for a function. Many candidates immediately added input() calls to ask for these values again, overwriting the parameters and losing marks. Examiners noted this was seen only from 'the most successful candidates' — use given parameters without adding inputs. The 2024 discriminator question was specifically designed to test this distinction.

J277/02

IPv6 addressing — format, group count, and separator character

J277/01 Q2(a)(i) June 2024: 'Many candidates found this question challenging with few candidates giving valid IP addresses.' IPv4 was more accurate; IPv6 was 'commonly inaccurate' with candidates giving 6 groups separated by full stops instead of 8 groups of 4 hexadecimal digits separated by colons. The distinction between IPv4 (four groups of denary values 0–255 separated by dots) and IPv6 (eight groups of 4 hexadecimal digits separated by colons) is a frequently tested gap.

J277/01

OS functions — peripheral management and the role of device drivers

J277/01 Q3(a) June 2024: 'Few candidates were able to identify a task performed by peripheral management. Candidates often rephrased peripheral management, for example stating that it managed the peripherals or managed the hardware without identifying what this involved.' The mark required naming device drivers as the mechanism by which the OS communicates with peripherals. Responses that simply restated the OS function name without describing the mechanism were not credited.

J277/01

Colour depth vs resolution — conflating increased colour depth with increased image resolution

J277/01 Q3(b)(iv) June 2023: a formal Misconception note stated 'a common misconception is that colour depth increases the resolution of the image'. Colour depth (bits per pixel) controls the number of possible colours — increasing it makes each pixel's colour more precise and increases file size, but does not change the number of pixels. Resolution is determined by the number of pixels in the image (width × height), not by colour depth. Candidates who confused these two properties consistently lost marks on image representation questions.

J277/01

Insertion sort algorithm — explaining why a condition-controlled loop is used for the inner loop

J277/02 Q3(b) June 2023: 'candidates generally found this question challenging. Many responses simply repeated the question and discussed sorting values.' The examiner noted that successful responses specifically explained that the inner loop moves the current element step by step until it reaches its correct position, and that a condition-controlled loop is necessary because the number of moves is unknown in advance — you stop when the element is in the right place, not after a fixed number of steps.

J277/02

Virtual memory — lack of precision about which storage type is used and how pages are involved

J277/01 Q5(a)(iii) June 2023 and Q7(b)(iii) June 2024: in 2023, changing the statement to 'primary storage' instead of 'RAM' was 'not precise enough to describe how VM works'. In 2024, stronger responses correctly noted that an embedded system is unlikely to have secondary storage and therefore cannot create virtual memory. Candidates need to state that VM uses secondary storage as an extension of RAM — not 'primary storage' in general, which includes ROM and cache.

J277/01

File handling in programs — combining procedure definitions with text file operations

J277/02 Q6(e) June 2023: 'this question proved to be challenging for many candidates. The question combined defining a procedure with the use of text files.' Examiners noted that 'full marks were often given where candidates appear to have had practical experience of these two techniques'. Candidates who lacked hands-on experience of writing to text files in a high-level language typically wrote a correct procedure structure but omitted the file open, write and close operations, or attempted to write file operations outside the procedure definition.

J277/02