2023 Cambridge IGCSE Computer Science (0478) Practice Paper with Answers

An 8-bit binary register contains the value `10101100`.

Identify the following:
1. The hexadecimal equivalent of this binary value.
2. The binary value after performing a logical shift right of 2 places.
3. The denary (base 10) value of the shifted binary representation from part 2.

Interrupts are crucial signals used in modern computer operating systems.

Describe three distinct scenarios (including the hardware or software trigger involved) that would generate an interrupt in a computer system.

A barcode scanner uses a check digit to ensure data is correctly read and processed.

1. State the primary purpose of a check digit.
2. State two different manual data entry errors that a check digit can detect.

A portable digital camera uses Solid-State Drive (SSD) storage instead of a magnetic Hard Disk Drive (HDD).

Explain three physical or operational reasons why solid-state storage is more suitable than magnetic storage for a portable digital camera.

Explain the purpose of an interrupt in a computer system and describe two different scenarios that would generate an interrupt.

Describe the role of the Program Counter (PC) and the Memory Address Register (MAR) during the Fetch stage of the Von Neumann fetch-decode-execute cycle.

A company is setting up a new network. They are choosing between serial half-duplex data transmission and parallel full-duplex data transmission.

Compare these two methods of data transmission by explaining how data is transmitted in each, and state one advantage of using serial half-duplex instead of parallel full-duplex.

Describe how a cyclic redundancy check (CRC) is used to detect errors in transmitted data.

A chemical plant uses an automated system to monitor and regulate the temperature of a reaction vessel.

Describe how sensors, microprocessors, and actuators are used in this automated closed-loop system to maintain the temperature within a safe range.

A computer system stores the denary value 154 as an 8-bit unsigned binary integer.

Show your working to:
1. Convert 154 to an 8-bit binary integer.
2. Perform a logical right shift of two places on the resulting binary integer.
3. Convert this shifted binary integer into hexadecimal.

An uncompressed bitmap image has a resolution of \(1024 \times 512\) pixels. The image is saved with a colour depth of 24 bits.

Calculate the file size of the image in Kibibytes (KiB). Show all your working.

A mono audio track is recorded with a sample rate of 16,000 Hz and a sample resolution of 16 bits. The duration of the recording is 32 seconds.

Calculate the size of the audio file in Kibibytes (KiB). Show all your working.

A data transmission uses a parity block (even parity) to check for errors. The following block of data is received:

Row 1: 1 0 1 1 0 0 1 0
Row 2: 0 1 1 0 1 1 0 0
Row 3: 1 1 0 0 0 1 1 1
Row 4: 0 0 1 1 1 0 0 1
Row 5 (Parity byte): 0 0 1 1 0 0 0 0

Identify the row and column of the single bit that has been transmitted incorrectly, explain how you located it, and state its corrected value.

The diagram shows some of the components and buses in a Central Processing Unit (CPU) based on the Von Neumann model.

```
+---------------+
| A |
+---------------+
|
v
+---------------+ +-------------+
| MAR | ===== C ======> | |
+---------------+ | |
| Main |
+---------------+ | Memory |
| B | <==== D =======> | |
+---------------+ +-------------+
|
v
+---------------+
| CIR |
+---------------+
```

Identify the labels **A**, **B**, **C**, and **D** in the diagram.

**A**: ................................................................

**B**: ................................................................

**C**: ................................................................

**D**: ................................................................

The diagram shows some of the components and buses in a Central Processing Unit (CPU) based on the Von Neumann model.

```
+---------------+
| A |
+---------------+
|
v
+---------------+ +-------------+
| MAR | ===== C ======> | |
+---------------+ | |
| Main |
+---------------+ | Memory |
| B | <==== D =======> | |
+---------------+ +-------------+
|
v
+---------------+
| CIR |
+---------------+
```

Identify the labels **A**, **B**, **C**, and **D** in the diagram.

**A**: ................................................................

**B**: ................................................................

**C**: ................................................................

**D**: ................................................................

An interrupt is a signal sent to the processor to request its attention. Which of the following statements about interrupts are true?

1. An interrupt can be generated by a hardware device (such as a printer running out of paper).
2. The processor must immediately stop executing the current program and shut down when any interrupt is received.
3. Interrupts allow for efficient multi-tasking by letting the CPU allocate time slices to different tasks.
4. When an interrupt is received, the current state of the CPU registers is saved before the Interrupt Service Routine (ISR) is executed.

A system uses a checksum to detect data transmission errors. The checksum is calculated by summing the byte values of the transmitted data and finding the remainder after dividing the sum by 256 (modulo 256).

The received data bytes are: 150, 42, 85, and 93. The transmitted checksum is 114.

Determine whether an error is detected, and identify a limitation of using a checksum for error detection.

Consider the following pseudocode algorithm:

DECLARE X, Y : INTEGER
X <- 1
Y <- 5
WHILE X < Y DO
X <- X + 2
Y <- Y + 1
ENDWHILE

What are the final values of X and Y after this pseudocode segment is executed?

A database table named 'Books' contains fields: Title, Genre, Price, and Stock.

A developer runs the following SQL query:
SELECT Title, Price FROM Books WHERE (Genre = "Sci-Fi" OR Genre = "Fantasy") AND Price < 15.00;

Which of the following database records would be returned by this query?

Consider the logic circuit represented by the following boolean expression:

\(X = \text{NOT}(A \text{ AND } B) \text{ AND } (A \text{ OR } B)\)

What are the resulting output values of \(X\) for the input combinations (A = 0, B = 1) and (A = 1, B = 1) respectively?

A 1-dimensional array named 'Scores' is initialized as follows:

Scores[1] <- 120
Scores[2] <- 150
Scores[3] <- 90
Scores[4] <- 200
Scores[5] <- 110

The following pseudocode algorithm is then executed:

FOR Index <- 2 TO 5
IF Scores[Index] < Scores[Index - 1] THEN
Scores[Index] <- Scores[Index - 1]
ENDIF
ENDFOR

What are the contents of the 'Scores' array after this execution?

A school's software team is developing an automated computer system to record and analyze student daily attendance.

(a) Define the term *decomposition* and explain how the team would apply it when designing this attendance system. [3]

(b) Define the term *abstraction* and describe one piece of student information that would be abstracted (ignored) when designing this specific system. [2]

(c) During the testing stage of the program development life cycle, different types of test data are used. Identify two different types of test data that could be used to verify the attendance input system, and provide an example of each. [2]

An algorithm is written in pseudocode below. It processes an array Data containing eight integer elements.

```text
DECLARE Data : ARRAY[1:8] OF INTEGER
Data[1] <- 12
Data[2] <- 5
Data[3] <- -3
Data[4] <- 8
Data[5] <- 12
Data[6] <- 0
Data[7] <- 7
Data[8] <- -1

Limit <- 4
Count <- 0

FOR Index <- 1 TO 8
Value <- Data[Index]
IF Value > Limit THEN
Limit <- Value - Limit
Count <- Count + 1
ELSE
Value <- Value * 2
Data[Index] <- Value
ENDIF
NEXT Index

OUTPUT "Count is ", Count
OUTPUT "Limit is ", Limit
```

(a) Complete the trace table for the pseudocode algorithm. [8 marks]

| Index | Value | Limit | Count | Data[2] | Data[3] | Data[4] | Data[8] | Output |
|---|---|---|---|---|---|---|---|---|
| | | 4 | 0 | | | | | |
| | | | | | | | | |
| | | | | | | | | |
| | | | | | | | | |
| | | | | | | | | |
| | | | | | | | | |
| | | | | | | | | |
| | | | | | | | | |
| | | | | | | | | |
| | | | | | | | | |
| | | | | | | | | |

(b) State the exact final outputs produced by this algorithm. [2 marks]

An industrial control system monitors a heating unit. The system has three inputs:
- \(S\) representing the System Status (1 if active, 0 if inactive)
- \(H\) representing the Heat Level (1 if high, 0 if normal)
- \(E\) representing the Emergency Switch (1 if pressed, 0 if not pressed)

An alarm, \(A\), is activated (outputs 1) under either of the following conditions:
- The system is active (\(S=1\)) AND the heat level is high (\(H=1\))
OR
- The emergency switch is pressed (\(E=1\)) AND the system is inactive (\(S=0\))

(a) Write a logic expression to represent the conditions for activating the alarm (\(A\)). [4 marks]

(b) Complete the truth table below for this control system. [4 marks]

| S | H | E | Output (A) |
|---|---|---|------------|
| 0 | 0 | 0 | |
| 0 | 0 | 1 | |
| 0 | 1 | 0 | |
| 0 | 1 | 1 | |
| 1 | 0 | 0 | |
| 1 | 0 | 1 | |
| 1 | 1 | 0 | |
| 1 | 1 | 1 | |

An algorithm is represented by the following flowchart description. The algorithm inputs a series of student marks (out of 100). It counts the number of passes (marks 50 and above) and the number of fails (marks below 50). It also calculates the average mark of the students who passed. The input process terminates when a sentinel value of -1 is entered.

[Flowchart Description]
- Step 1: START
- Step 2: PassCount = 0, FailCount = 0, PassTotal = 0
- Step 3: INPUT Mark
- Step 4: Decision: Is Mark = -1?
- If YES: Go to Step 10
- If NO: Go to Step 5
- Step 5: Decision: Is Mark < 0 OR Mark > 100?
- If YES: OUTPUT "Error: Invalid Mark", then INPUT Mark, then go back to Step 4
- If NO: Go to Step 6
- Step 6: Decision: Is Mark >= 50?
- If YES: Go to Step 7
- If NO: Go to Step 8
- Step 7: PassCount = PassCount + 1, PassTotal = PassTotal + Mark, then go to Step 9
- Step 8: FailCount = FailCount + 1, then go to Step 9
- Step 9: INPUT Mark, then go back to Step 4
- Step 10: Decision: Is PassCount > 0?
- If YES: PassAverage = PassTotal / PassCount, OUTPUT "Passed:", PassCount, "Failed:", FailCount, "Average Pass:", PassAverage, then go to Step 11
- If NO: OUTPUT "Passed:", PassCount, "Failed:", FailCount, "No students passed", then go to Step 11
- Step 11: END

(a) Complete the trace table for the following input data:
55, 30, 105, 45, 75, -1

| Mark | PassCount | FailCount | PassTotal | PassAverage | OUTPUT |
|------|-----------|-----------|-----------|-------------|--------|
| | | | | | |

(b) The algorithm needs to be modified so that it also counts the number of "distinctions". A distinction is defined as a mark of 85 or above. Explain the modifications required to the steps of the flowchart to implement this new feature.

(c) Identify one example of each of the following types of test data that could be used to test the validation check (Step 5):
1. Normal test data
2. Extreme test data
3. Boundary test data (at the upper limit)
4. Abnormal test data
For each example, state the expected outcome of the validation check.

A database table, BIKE_RENTAL, is used to store details of bicycle rentals in a city. Here is a sample of the data in the table: | RentalID | BikeType | HourlyRate | DailyRental | DateRented | DurationHours | | BK091 | Electric | 8.50 | False | 12/05/2023 | 4 | | BK104 | Mountain | 5.00 | False | 12/05/2023 | 2 | | BK112 | Electric | 8.50 | True | 13/05/2023 | 10 | | BK115 | Road | 6.00 | False | 14/05/2023 | 1 | | BK120 | Electric | 8.50 | False | 14/05/2023 | 5 | (a) (i) State the field that should be chosen as the primary key. [1 mark] (ii) Give a reason for your choice in part (a)(i). [1 mark] (b) State the most appropriate data type for each of the following fields: (i) DailyRental [1 mark] (ii) HourlyRate [1 mark] (iii) DateRented [1 mark] (c) Write an SQL query to display the RentalID and DurationHours fields for all records where the BikeType is 'Electric' and the DurationHours is greater than 3. The output must be sorted in descending order of DurationHours. [4 marks] (d) State the name of a validation check that can be performed on the DurationHours field to ensure that values entered are between 1 and 24 inclusive. [1 mark]

A theatre uses a 2D array, SeatingPlan[1:10, 1:12], of type String to manage its seat reservations. The theatre has 10 rows, and each row has 12 seats.

Each element in the array contains either the string "Empty" if the seat is available, or a unique customer BookingID (e.g. "BK942") if the seat is already reserved.

Write an algorithm in pseudocode that meets the following requirements:
- Prompts the user to enter their unique BookingID. It must validate that the input is not empty, and re-prompt until a non-empty string is entered.
- Prompts the user to enter a row number and a seat number.
- Allows the user to cancel the booking process by entering -1 for the row number.
- Validates that the row number is between 1 and 10 (or -1 to cancel), and the seat number is between 1 and 12. If an input is invalid, it outputs an error message and prompts the user to try again.
- If the inputs are valid, checks if the selected seat is empty:
- If it is "Empty", reserves the seat by writing the BookingID to that position in the array, outputs a confirmation message, and ends the booking loop.
- If it is already reserved, outputs a message stating the seat is taken, and loops back to allow the user to choose another seat.
- Once the booking process is complete (either booked successfully or cancelled), the algorithm must count and output:
- The total number of booked seats currently in the theatre.
- The total number of empty seats remaining in the theatre.

You must declare all variables used in your algorithm. Assume the SeatingPlan array has already been created and populated with either "Empty" or existing booking IDs before your algorithm runs.