An original Thinka practice paper modelled on the structure and difficulty of the Nov 2023 (V2) Cambridge IGCSE Computer Science (0478) paper. Not affiliated with or reproduced from Cambridge.
Paper 12: Computer Systems
Answer all questions. Calculators must not be used. Total marks: 75. Questions cover computer hardware, storage, networking, security, data transmission, and automated systems.
13 题目 · 50.5 分
题目 1 · Matching
1.5 分
Identify the type of memory (RAM, ROM, or Cache) from the following descriptions: [1] Volatile memory used to temporarily store data and instructions currently being processed by the CPU. [2] High-speed volatile memory that stores frequently used CPU instructions to speed up processing. [3] Non-volatile memory containing the start-up instructions (bootstrap loader) that cannot be altered under normal operation.
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解题
1 corresponds to RAM because it is volatile and stores active processes. 2 corresponds to Cache because it is high-speed and stores frequently used instructions. 3 corresponds to ROM because it is non-volatile and holds boot instructions.
评分标准
0.5 marks for each correct identification: 1 is RAM, 2 is Cache, 3 is ROM.
题目 2 · Matching
1.5 分
Identify the cyber security threat described in each scenario: [1] An email is sent to a user pretending to be from their bank, containing a link to a fake website designed to steal login credentials. [2] Malicious software that encrypts a user's files and demands a payment to decrypt them. [3] A program that appears to be useful or harmless software but contains hidden malicious code that executes in the background.
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解题
1 is Phishing as it uses fake emails/websites to steal credentials. 2 is Ransomware as it encrypts files for ransom. 3 is a Trojan horse as it disguises itself as legitimate software.
评分标准
0.5 marks for each correct identification: 1 is Phishing, 2 is Ransomware, 3 is Trojan horse.
题目 3 · Matching
1.5 分
Identify the most suitable sensor from the list (Temperature, Light, Ultrasonic, or Flow) for each automated scenario: [1] Detecting if an intruder has broken a light beam in a security system. [2] Monitoring the temperature of an industrial oven to ensure it does not overheat. [3] Checking if a driver has parked a car too close to a wall by measuring distance.
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解题
1 uses a Light sensor to detect a broken beam. 2 uses a Temperature sensor to monitor oven heat. 3 uses an Ultrasonic sensor to measure distance to a wall.
评分标准
0.5 marks for each correct identification: 1 is Light, 2 is Temperature, 3 is Ultrasonic.
题目 4 · Matching
1.5 分
Identify the category of software (Operating System, Utility, or Application) described in each statement: [1] Software that manages the computer's hardware, files, and memory, and provides a user interface. [2] Software designed to help analyze, configure, optimize or maintain a computer, such as disk defragmenters. [3] Software created to perform specific user-oriented tasks, such as word processing or photo editing.
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解题
1 is Operating System because it manages hardware and resources. 2 is Utility because it assists in maintenance and optimization. 3 is Application because it performs specific user tasks.
评分标准
0.5 marks for each correct identification: 1 is Operating System, 2 is Utility, 3 is Application.
题目 5 · Matching
1.5 分
Identify the error detection method (Checksum, Check digit, or Parity check) described in each scenario: [1] A calculation is performed on the digits of an identification number (such as a barcode) to produce a final digit that verifies its entry. [2] A calculation is done on a block of data to generate a value, which is sent along with the data and compared at the destination; if they differ, retransmission is requested. [3] A bit is appended to a byte of data to make the total count of 1-bits either even or odd.
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解题
1 is a Check digit as it calculates an extra digit for identification numbers. 2 is a Checksum as it applies to blocks of data to verify integrity. 3 is a Parity check as it counts and sets 1-bits to even or odd.
评分标准
0.5 marks for each correct identification: 1 is Check digit, 2 is Checksum, 3 is Parity check.
题目 6 · Structured Explanation
4 分
A computer system uses the Von Neumann model. When an instruction is fetched, several registers inside the Central Processing Unit (CPU) are utilized. Explain the specific roles of the Program Counter (PC) and the Memory Data Register (MDR) during the fetch stage of the fetch-decode-execute cycle.
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解题
The Program Counter (PC) holds the address of the next instruction to be fetched from memory. This address is copied from the PC to the Memory Address Register (MAR) via the address bus. The PC is then incremented to point to the address of the next sequential instruction. The Memory Data Register (MDR) temporarily stores the instruction or data that has been fetched from the memory location specified by the MAR.
评分标准
Max 2 marks for Program Counter (PC): - 1 mark: Holds the address of the next instruction to be fetched. - 1 mark: Passes/copies this address to the MAR OR is incremented after the address is sent.
Max 2 marks for Memory Data Register (MDR): - 1 mark: Temporarily stores the instruction/data fetched from memory. - 1 mark: Receives data/instruction via the data bus OR passes it to the Current Instruction Register (CIR).
题目 7 · Structured Explanation
5 分
Data transmission can be classified by direction (simplex, half-duplex, full-duplex) and by method (serial, parallel). A manufacturing plant needs to send sensor readings continuously from a remote warehouse to a central control computer located 2 kilometres away. State and explain the most suitable combination of transmission direction and transmission method for this application.
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解题
Direction: Simplex transmission. Data only needs to travel in one direction, from the remote warehouse sensor to the central control computer; there is no requirement for feedback or control signals to be sent back to the sensor in this specific scenario. Method: Serial transmission. The distance is 2 km, which is a long distance; serial transmission is more reliable and less prone to data skewing over long distances than parallel transmission. Additionally, serial is cheaper to install because it only requires a single wire/channel compared to the multiple wires required for parallel transmission.
评分标准
- 1 mark: Identifies simplex as the suitable direction. - 1 mark: Explains simplex: data only flows in one direction / from sensor to computer. - 1 mark: Identifies serial as the suitable method. - 1 mark: Explains serial suitability regarding distance: more reliable over long distances / less prone to signal attenuation/skewing. - 1 mark: Explains serial suitability regarding cost: cheaper to install over 2 km as it requires fewer wires.
题目 8 · Structured Explanation
4 分
A bank wants to protect its online customers from pharming attacks. Explain how a pharming attack is carried out and describe one way a customer can identify if they have been directed to a fake website.
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解题
Pharming is carried out when malicious code/malware is downloaded onto the user's device or the DNS server database is corrupted/poisoned. This causes the redirection to occur automatically when the user types in a legitimate URL, landing them on a fake website. To identify a fake website, a user can check the URL in the address bar carefully for slight spelling variations, or look for the padlock symbol and 'https://' in the address bar indicating a secure, verified SSL/TLS connection.
评分标准
Max 2 marks for how pharming is carried out: - 1 mark: Malicious code/malware is downloaded onto the user's device OR the DNS server database is corrupted/poisoned. - 1 mark: Redirection occurs automatically when the user types in a legitimate URL.
Max 2 marks for how to identify the fake website: - 1 mark: Look for the padlock symbol / 'https://' in the address bar. - 1 mark: Check the domain name carefully for slight spelling variations OR check/verify the SSL/TLS certificate details.
题目 9 · Structured Explanation
5 分
An automated greenhouse system controls the temperature to keep it within a range of 18 degrees Celsius to 25 degrees Celsius. The system uses a temperature sensor, a microprocessor, and a heating element. Explain how the sensor, microprocessor, and heating element work together to maintain the temperature within the required range.
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解题
The temperature sensor continuously takes readings of the greenhouse temperature. These analogue readings are converted to digital signals using an Analogue-to-Digital Converter (ADC) so the microprocessor can process them. The microprocessor compares the received digital temperature values against the pre-stored range of 18 degrees Celsius to 25 degrees Celsius. If the temperature is below 18 degrees Celsius, the microprocessor sends a signal to turn on the heating element (via an actuator). If the temperature is above or within the range, the microprocessor sends a signal to turn off or keep off the heating element. This cycle repeats continuously.
评分标准
- 1 mark: Sensor continuously measures temperature and sends data to an ADC. - 1 mark: Microprocessor receives digital data and compares it to pre-stored range/values (18 and 25). - 1 mark: If temperature is below 18 degrees Celsius, microprocessor sends a signal to turn on the heating element. - 1 mark: If temperature is above or within range, microprocessor sends a signal to turn off/keep off the heating element. - 1 mark: Explains that this process is continuous / operates in a continuous loop.
题目 10 · Structured Explanation
4 分
When a user types a web address into their browser, the Domain Name System (DNS) is used to find the corresponding IP address. Explain how the browser and the DNS work together to locate and load the requested web page.
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解题
The browser requests the IP address for the domain name from the local DNS server. The DNS server searches its database or registry for the matching IP address of that domain name. If found, the DNS server sends the IP address back to the browser. The browser then uses the returned IP address to send an HTTP/HTTPS request directly to the web server hosting the website.
评分标准
- 1 mark: Browser sends the domain name / URL to the DNS server. - 1 mark: DNS server searches its database to find the matching IP address. - 1 mark: DNS server returns/sends the IP address back to the browser. - 1 mark: Browser uses this IP address to request the website files/data from the web server.
题目 11 · Structured Explanation
5 分
A graphic designer's computer has 8 GB of Random Access Memory (RAM). While running multiple heavy design applications, the RAM becomes full, and the operating system starts using virtual memory. Explain how virtual memory is used to allow the computer to continue running the applications, and describe one disadvantage of relying on virtual memory.
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解题
Virtual memory is created by partitioning a section of secondary storage (HDD/SSD) to act as temporary RAM. When RAM is full, the operating system identifies inactive pages or blocks of data currently in RAM. These inactive pages are transferred/copied from RAM to the virtual memory space on the secondary storage. This frees up physical RAM for the active processes currently needed by the CPU. When the processor needs this data again, it is swapped back into RAM, and other inactive pages are moved out. Disadvantage: Relying on virtual memory significantly slows down system performance because the read/write speeds of secondary storage are much slower than RAM, which can also cause disk thrashing.
评分标准
Max 4 marks for explanation of how virtual memory is used: - 1 mark: Partition/allocation of space is created on secondary storage (HDD/SSD) to act as temporary memory. - 1 mark: When RAM is full, the operating system moves/transfers inactive pages of data from RAM to this partition. - 1 mark: This frees up space in physical RAM for the active processes currently needed by the CPU. - 1 mark: If the transferred data is required again, it must be swapped back into RAM (by swapping out other data).
Max 1 mark for disadvantage: - 1 mark: Secondary storage is much slower than physical RAM, leading to slower performance / disk thrashing.
题目 12 · Calculation
8 分
An 8-bit CPU register stores the following binary value representing a system reading: 1 0 1 0 1 1 0 0. (a) (i) Convert the binary number in the register to denary. Show your working. (ii) Convert the binary number in the register to hexadecimal. Show your working. (b) A negative temperature of -76 degrees Celsius needs to be stored in an 8-bit register using two's complement. Convert -76 into an 8-bit binary number. Show your working. (c) A logical left shift of two places is performed on the original binary value stored in the register (10101100). State the binary contents of the register after this shift has been performed.
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解题
(a) (i) 128 + 32 + 8 + 4 = 172. (ii) Split into two 4-bit nibbles: 1010 and 1100. 1010 in binary is 10 in denary, which is A in hex. 1100 in binary is 12 in denary, which is C in hex. Thus, the hexadecimal value is AC. (b) Positive 76 in binary is 01001100. Inverting the bits (one's complement) gives 10110011. Adding 1 gives the two's complement representation: 10110100. (c) Shifting 10101100 left by two places discards the leftmost two bits (1 and 0), moves all other bits two positions to the left, and inserts two 0s on the right, resulting in 10110000.
评分标准
(a) (i) [2 marks] - 1 mark for correct working showing addition of place values (128 + 32 + 8 + 4) - 1 mark for correct denary value: 172. (ii) [2 marks] - 1 mark for showing correct split into nibbles or converting to denary values 10 and 12 - 1 mark for correct hexadecimal value: AC. (b) [2 marks] - 1 mark for correct method of finding two's complement (e.g., showing +76 in binary as 01001100, then inverting and adding 1, or subtracting 76 from 256) - 1 mark for correct final binary value: 10110100. (c) [2 marks] - 1 mark for shifting bits correctly by two positions - 1 mark for padding the empty right positions with two zeros: 10110000.
题目 13 · Table Completion
8 分
Data transmission can sometimes result in errors. Various error detection methods are used to identify if data has been corrupted during transmission. (a) Complete the table below by identifying the missing error detection method or providing the missing description. Row 1: Method name is (i) [1 mark]; Description is: A digit calculated from the other digits in a numerical identifier (such as a barcode or ISBN). It is appended to the data and used to verify that the identification number is valid and has been entered correctly. Row 2: Method name is Checksum; Description is (ii) [2 marks]. Row 3: Method name is (iii) [1 mark]; Description is: A basic error detection method where an extra bit is added to a byte of data before transmission to ensure the total number of 1-bits is either always odd or always even. Row 4: Method name is Automatic Repeat Query (ARQ); Description is (iv) [2 marks]. (b) An 8-bit byte of data is transmitted using even parity: 1 1 0 1 0 1 0 X. Identify the correct value for the missing parity bit, X, in the rightmost position. State the reason for your choice. [2 marks]
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解题
(a) (i) Check digit is calculated from the digits of an identification number to verify input or transmission accuracy. (ii) Checksum description: A mathematical sum computed from a block of data, transmitted with the block, and compared at the receiving end to detect any transmission errors. (iii) Parity check uses a parity bit (odd or even) to detect single-bit errors in a byte. (iv) ARQ description: A system where the receiver checks data packets for errors and, if found (or if a packet is lost), uses acknowledgments and timeout mechanisms to automatically request the sender to retransmit the corrupted or missing packets. (b) X = 0. In the byte 1 1 0 1 0 1 0 X, there are currently four 1s. Since 4 is already an even number, X must be 0 to maintain an even number of 1s in the byte.
评分标准
(a) (i) [1 mark] - 1 mark for: Check digit (accept: checkdigit). (ii) [2 marks] - 1 mark for identifying that a value is calculated from the block of data - 1 mark for describing that it is sent with the data and recalculated/compared at the destination. (iii) [1 mark] - 1 mark for: Parity check / Parity bit. (iv) [2 marks] - 1 mark for mentioning the use of acknowledgments (ACK/NAK) and/or timeouts - 1 mark for stating that the sender automatically retransmits the data if an error is detected or timeout occurs. (b) [2 marks] - 1 mark for identifying the correct parity bit value: 0 - 1 mark for correct explanation stating that there are four 1s (which is an even number), so the parity bit must be 0 to keep the total count of 1s even.
Answer all questions. Calculators must not be used. Total marks: 75. Questions require pseudocode construction, tracing, debugging, logic evaluation, databases, and structural modifications.
7 题目 · 48 分
题目 1 · written
5 分
An algorithm is represented by the following pseudocode:
Count <- 0 Total <- 0 INPUT Num WHILE Num <> -1 DO IF Num > 10 THEN Total <- Total + Num Count <- Count + 1 ENDIF INPUT Num ENDWHILE IF Count > 0 THEN Average <- Total / Count OUTPUT "Average: ", Average ELSE OUTPUT "No numbers" ENDIF Complete the trace table for the input data: 12, 5, 18, 9, -1
One mark for each correct column (max 5 marks): - Num column: 12, 5, 18, 9, -1 in correct positions (1 mark) - Count column: 0, 1, 2 in correct positions (1 mark) - Total column: 0, 12, 30 in correct positions (1 mark) - Average column: 15 in correct position (1 mark) - OUTPUT column: "Average: 15" (1 mark)
题目 2 · written
5 分
An algorithm is represented by the following pseudocode:
Word <- "REVISION" NewWord <- "" Len <- LENGTH(Word) FOR i <- Len TO 1 STEP -2 Char <- SUBSTRING(Word, i, 1) NewWord <- NewWord + Char NEXT i OUTPUT NewWord The function LENGTH(str) returns the number of characters in the string str. The function SUBSTRING(str, start, length) returns a portion of str starting at position start with the specified length. The first character of the string is at position 1.
One mark for each correct column (max 5 marks): - Word, Len and initial NewWord correct (1 mark) - i column correctly showing step down (8, 6, 4, 2) (1 mark) - Char column correctly extracting characters ("N", "I", "I", "E") (1 mark) - NewWord column correctly updated with concatenation (1 mark) - OUTPUT column showing final output correctly (1 mark)
题目 3 · written
5 分
A one-dimensional array Data[1:5] contains the following values: [14, 25, 9, 14, 30]
An algorithm is represented by the following pseudocode:
Target <- 14 FoundCount <- 0 FOR Index <- 1 TO 5 IF Data[Index] = Target THEN FoundCount <- FoundCount + 1 Pos[FoundCount] <- Index ENDIF NEXT Index OUTPUT "Found at ", FoundCount, " positions" Complete the trace table for this algorithm.
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解题
The completed trace table should be as follows:
TargetIndexFoundCountPos[1]Pos[2]OUTPUT140111234245Found at 2 positions
评分标准
One mark per marking point (max 5 marks): - Target initialized to 14, Index correctly looping from 1 to 5 (1 mark) - FoundCount updated from 0 to 1 and then to 2 (1 mark) - Pos[1] correctly storing 1 (1 mark) - Pos[2] correctly storing 4 (1 mark) - OUTPUT showing the exact final output message (1 mark)
题目 4 · structured
6 分
A database table named VinylRecords contains information about albums in a music store. The fields in the table are CatalogNumber, AlbumTitle, Musician, YearOfRelease, StockQty, and UnitPrice.
(a) Identify the field that would make the most appropriate primary key. Explain why this field is suitable. [2 marks]
(b) Write a Structured Query Language (SQL) query to retrieve the AlbumTitle, Musician, and UnitPrice of all records where the StockQty is less than 5 and YearOfRelease is greater than 2015. [4 marks]
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解题
(a) The CatalogNumber is chosen as the primary key because it uniquely identifies each specific vinyl record in the inventory, preventing duplicates.
(b) The SQL statement uses SELECT to retrieve the requested fields (AlbumTitle, Musician, UnitPrice), FROM to define the target table (VinylRecords), and WHERE to apply the combined conditional filters using the AND operator (StockQty < 5 AND YearOfRelease > 2015).
评分标准
Part (a): - 1 mark for identifying CatalogNumber. - 1 mark for explaining that it contains unique values for each record.
Part (b): - 1 mark for SELECT AlbumTitle, Musician, UnitPrice - 1 mark for FROM VinylRecords - 1 mark for WHERE StockQty < 5 - 1 mark for AND YearOfRelease > 2015 (order of conditions can be reversed).
题目 5 · structured
6 分
A database table named FlightDetails stores outgoing flight information with the following fields: FlightID, Destination, DepartureTime, GateNumber, and IsDelayed (Boolean).
(a) Write a Structured Query Language (SQL) query to display the FlightID and GateNumber for all flights going to 'Paris' where IsDelayed is True. [3 marks]
(b) Describe the modifications needed to this database structure if the operator wants to store the passenger capacity (whole number up to 300) and ticket cost (with decimals) for each flight. [3 marks]
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解题
(a) The SQL query filters the records using SELECT to specify FlightID and GateNumber, FROM to choose the FlightDetails table, and WHERE with the criteria Destination = 'Paris' AND IsDelayed = True.
(b) To store the new details, the database schema must be modified. You need to add a field for passenger capacity, defined as an Integer data type (since capacity is a whole number), and a field for ticket cost, defined as a Real data type (since cost requires decimal places).
评分标准
Part (a): - 1 mark for SELECT FlightID, GateNumber - 1 mark for FROM FlightDetails - 1 mark for WHERE Destination = 'Paris' AND IsDelayed = True (or IsDelayed = Yes)
Part (b): - 1 mark for stating that a field for passenger capacity must be added with an Integer data type. - 1 mark for stating that a field for ticket cost must be added with a Real data type. - 1 mark for stating that the table structure/schema must be altered to accommodate these new fields.
题目 6 · structured
6 分
A school library uses a database table named BookInventory with the following fields: ISBN, Title, BorrowCount, and Available.
(a) Complete the list by stating the most appropriate database data type for each of these fields: Title, BorrowCount, Available. Each data type you choose must be different. [3 marks]
(b) Write an SQL query to retrieve the Title and ISBN of all books that have a BorrowCount greater than 50 and are currently not Available. [3 marks]
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解题
(a) The fields represent different data types: Title holds text characters (text), BorrowCount stores a whole count of transactions (integer), and Available indicates one of two states (Boolean).
(b) The SQL query is built with: SELECT Title, ISBN, FROM BookInventory, and WHERE BorrowCount > 50 AND Available = False (or NOT Available).
评分标准
Part (a): - 1 mark for Title: text - 1 mark for BorrowCount: integer - 1 mark for Available: Boolean
Part (b): - 1 mark for SELECT Title, ISBN - 1 mark for FROM BookInventory - 1 mark for WHERE BorrowCount > 50 AND Available = False (accept Available = No or NOT Available)
题目 7 · subjective
15 分
A bicycle rental shop stores the names of up to 150 customers in a one-dimensional (1D) array Customers[]. A two-dimensional (2D) array Rentals[] stores details of each customer's rental: - rental duration in hours (one decimal place) - choice of bike index (whole number) - helmet choice index (1 for Yes, 2 for No) - price of rental in dollars (two decimal places)
The rental duration must be between 1.0 and 8.0 hours inclusive. The index of any customer's data is the same in both arrays. For example, a customer named in index 10 of Customers[] corresponds to the data in index 10 of Rentals[].
The bicycle choices available are: Index 1: Road Bike ($12.50 per hour) Index 2: Mountain Bike ($15.00 per hour) Index 3: Electric Bike ($22.00 per hour)
If the customer chooses to rent a helmet, an additional flat fee of $5.00 is added to the total cost.
The data for bicycle types and hourly rates are stored in two 1D arrays named BikeType[] and HourlyRate[]. The index of the bicycle type and hourly rate in their arrays share the same index number.
Write a program that meets the following requirements: - initialise the arrays BikeType[] and HourlyRate[] - input a new customer's name, rental duration, and helmet choice - check that the rental duration is valid; output an error message and require the duration to be re-entered until it is valid - input the choice of bicycle and find its hourly rate; validate that the choice is 1, 2, or 3, re-entering if invalid - calculate the total price of the rental (duration multiplied by hourly rate plus helmet fee if rented) - store all data in the relevant arrays - output the customer's rental receipt to include: the name of the customer, the type of bicycle, helmet rented (Yes/No), and the total calculated cost - continue to accept the next customer until a customer name of 'END' is entered or the array limit of 150 is reached.
You must use pseudocode or program code and add comments to explain how your code works. You do not need to declare any arrays or variables; you may assume that this has already been done.
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解题
The solution requires a structured looping program that initialises lookup arrays, prompts for inputs, validates them through standard pre-condition validation loops (WHILE loops), computes total cost dynamically using conditional additions, updates parallel data structures, and outputs receipts cleanly until termination criteria are met.
评分标准
AO2: Apply knowledge and understanding (Max 9 marks) - R1: Input and validation (Max 3 marks) * 1 mark for inputting customer name and checking for 'END' termination * 1 mark for rental duration validation loop (1.0 to 8.0 inclusive) * 1 mark for bike choice validation loop (1, 2, or 3) - R2: Initialisation and calculation (Max 3 marks) * 1 mark for initialising BikeType and HourlyRate arrays correctly * 1 mark for calculating cost correctly with dynamic addition of helmet fee * 1 mark for saving inputs correctly in parallel 1D and 2D arrays - R3: Logic and receipt output (Max 3 marks) * 1 mark for main loop continuing until limit of 150 or 'END' entered * 1 mark for incrementing customer index pointer correctly * 1 mark for outputting customer name, bike type text description, helmet option, and cost
AO3: Provide solutions (Max 6 marks) - 5-6 marks: Clean, fully commented program with highly descriptive identifiers, logical ordering, and absolute syntax correctness. - 3-4 marks: Solution with some comments, mostly meaningful identifiers, minor structural or logical omissions. - 1-2 marks: Minimal documentation, unhelpful variable names, significant logic flaws.
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