2021 HKDSE Information and Communication Technology Practice Paper | DSE Mock

What is the decimal value represented by the 8-bit binary string after performing the addition \(01011100_2 + 00111010_2\) in an 8-bit signed two's complement system?

Consider the following algorithm in pseudocode:\n\n```\nA = 5\nB = 3\nC = 0\nWhile A > 0 do\n If A mod 2 == 1 then\n C = C + B\n B = B * 2\n A = A div 2\n```\n\nWhat is the value of `C` when the algorithm finishes?

Which of the following statements about cache memory in a computer system are correct?\n\n(1) Cache memory is faster than RAM but slower than CPU registers.\n(2) Cache memory is non-volatile.\n(3) Cache memory stores frequently used data and instructions to speed up CPU processing.

An IP address is `192.168.10.45` with a subnet mask of `255.255.255.240`. Which of the following IP addresses is in the same subnet as this IP address?

Consider the following database schema for a school enrollment system:\n\n`STUDENT(StudentID, StudentName, Class)`\n`COURSE(CourseID, CourseName, Teacher)`\n`ENROLLMENT(StudentID, CourseID, EnrollDate, Grade)`\n\nWhich of the following statements is/are correct?\n\n(1) The primary key of `ENROLLMENT` should be the composite key `(StudentID, CourseID)`.\n(2) `StudentID` in `ENROLLMENT` is a foreign key referencing `STUDENT`.\n(3) `StudentID` in `STUDENT` must be unique and cannot contain null values.

In a spreadsheet, cell `B2` contains the formula `=$A$1 + B1`. If this formula is copied and pasted into cell `D4`, what will the formula in `D4` be?

If Alice wants to send a confidential message to Bob using public key cryptography, which key should Alice use to encrypt the message, and which key should Bob use to decrypt it?

Which of the following are advantages of RFID technology over traditional optical barcodes?\n\n(1) RFID tags can be read without a direct line of sight.\n(2) Multiple RFID tags can be scanned and identified simultaneously.\n(3) RFID tags can store larger amounts of data and many can be read/written multiple times.

A student wrote a program to find the average of three positive integers. The program executed without any error messages, but it printed `7` instead of `5` when the inputs were `3`, `5`, and `7`. What type of error is this?

An uncompressed stereo (2 channels) audio track is recorded with a sampling rate of \(44.1 \text{ kHz}\) and a bit depth of \(16 \text{ bits}\). What is the file size of a 2-minute recording in megabytes (MB)? (Assume \(1 \text{ MB} = 10^6 \text{ bytes}\))

An 8-bit register represents signed integers using two's complement representation. What is the decimal value represented by the binary string \(11001011_2\)?

Which of the following statements about CPU cache memory is/are correct? (1) It is faster than DRAM but slower than CPU registers. (2) It uses SRAM. (3) It stores the most frequently used data and instructions to reduce the average cost of access from the main memory.

A computer has an IP address of \(192.168.10.45\) and a subnet mask of \(255.255.255.224\). Which of the following IP addresses is on the same local subnet as this computer?

Consider the following pseudocode segment: `X = 7`, `Y = 3`, `result = 0`. `while X > 0 do:` `if X % 2 != 0 then result = result + Y`, `X = X div 2`, `Y = Y * 2`. What is the value of `result` after execution? (Note: `div` represents integer division and `%` represents the modulo operator.)

In a spreadsheet, cell B2 contains the formula `=$A2 + B$1`. If cell B2 is copied and pasted into cell D4, what formula will be displayed in cell D4?

Consider two relational database tables: `STUDENT` (`StudentID`, `Name`, `ClassID`) where `StudentID` is the primary key and `ClassID` is a foreign key referencing the `CLASS` table, and `CLASS` (`ClassID`, `ClassName`, `Teacher`) where `ClassID` is the primary key. Which of the following operations violates referential integrity?

Alice wants to send an encrypted message to Bob to ensure confidentiality, and she also wants to attach a digital signature to guarantee the authenticity of the message. To achieve both confidentiality and authenticity, Alice should encrypt the message and create the digital signature using which keys?

A program accepts an integer input \(N\) representing a student's mark (\(0 \le N \le 100\)). It outputs "Pass" if \(N \ge 50\) and "Fail" otherwise. A programmer wants to perform Boundary Value Analysis (BVA) to design test cases. Which of the following sets of values for \(N\) represents the best boundary test cases?

Which of the following is an example of a data verification method rather than a data validation method?

Which of the following are advantages of Radio Frequency Identification (RFID) technology over Barcode technology? (1) RFID tags can be read without a direct line of sight. (2) Multiple RFID tags can be scanned simultaneously. (3) RFID tags can store read-write data, whereas traditional barcodes are read-only.

In an 8-bit two's complement binary system, what is the representation of the decimal value \(-43\)?

Which of the following statements about cache memory in a computer system is/are correct?
(1) Cache memory is faster than RAM because it is located closer to or inside the CPU.
(2) Cache memory has a larger capacity than RAM to store more executing program instructions.
(3) Cache memory is non-volatile, retaining data even when the computer is powered off.

Consider the following algorithm written in pseudocode:
```
X = 14
Y = 4
result = 0
while X >= Y do
X = X - Y
result = result + 1
endwhile
```
What are the values of `X` and `result` after the execution of the algorithm?

A company wants to assign IP addresses to its host computers. Which of the following IP addresses can be assigned to a host computer on a private local area network (LAN)?

A spreadsheet contains the following data:
- Cell A1: 10, Cell B1: 2
- Cell A2: 20, Cell B2: 4
- Cell A3: 30, Cell B3: 5

The formula `=$A1+B$1` is entered in cell C1 and then copied to cell D3. What is the value displayed in cell D3?

An audio file is recorded with a sampling rate of 44.1 kHz, 16-bit resolution, and in stereo (2 channels). What is the estimated file size, in megabytes (MB), of a 5-minute uncompressed recording?

During the fetch stage of the machine cycle, which register stores the address of the next instruction to be executed?

An array of 1,000 elements is sorted in ascending order. If we use the binary search algorithm to search for a specific target value in this array, what is the maximum number of comparisons needed?

When a smartphone connects to a public Wi-Fi network, which protocol is responsible for automatically assigning a temporary IP address, subnet mask, and default gateway to the device?

To ensure the accuracy of data entry in a database, a developer implements two measures:
(1) Entering the password twice during registration to ensure they match.
(2) Checking if the entered age is a positive integer between 0 and 150.

Which types of data checks are (1) and (2) respectively?

An 8-bit register stores integers in 2's complement representation. What is the result in decimal when the bitwise XOR operation is performed between the representation of -18 and 35, and then interpreted as a signed 8-bit integer?

Consider the following pseudo-code:

`X = 0`
`For I from 1 to 4:`
` For J from I to 4:`
` If (I + J) is even then:`
` X = X + I`
` Else:`
` X = X + J`

What is the value of `X` after executing the algorithm?

A computer system is upgraded by increasing its data bus width from 32-bit to 64-bit, while the clock frequency is reduced from \(3.2 \text{ GHz}\) to \(2.0 \text{ GHz}\). Assuming that the CPU can fetch one word per bus cycle and all other factors remain constant, what is the ratio of the theoretical maximum data transfer rate of the new system's data bus to that of the old system?

An organization is assigned the IP address range 192.168.10.0/24. If they need to divide this network into exactly 4 subnets of equal size, which of the following represents the valid subnet mask and the maximum number of usable host IP addresses in each subnet?

In a spreadsheet, cell A1 contains the formula `=$B1+C$2`. If we copy this formula and paste it into cell D3, what is the formula in D3?

Alice wants to send a confidential and digitally signed document to Bob using asymmetric key cryptography. Which keys should Alice use to sign the document and encrypt the document respectively?

Which of the following statements about disk defragmentation is/are correct?

(1) It reduces the physical distance the read/write head of a Solid State Drive (SSD) needs to move, thereby extending its lifespan.
(2) It reorganizes fragmented files into contiguous sectors to improve file access speed on Hard Disk Drives (HDDs).
(3) It increases the total unused storage capacity of the disk by compressing system files.

In a relational database, there are two tables: `STUDENT` and `CLASS`. The primary key of `CLASS` is `ClassID`. The `STUDENT` table has a foreign key `ClassID` that references the `CLASS` table. Which of the following operations would violate referential integrity?

(1) Inserting a new record into `STUDENT` with a `ClassID` that does not exist in `CLASS`.
(2) Deleting a record from `CLASS` when there are student records referencing that `ClassID`.
(3) Updating a student's `ClassID` to `NULL`, assuming nullable constraints allow it.

Which of the following tasks should be processed using server-side scripting rather than client-side scripting?

(1) Validating that an email input field contains an '@' symbol before submission.
(2) Verifying user credentials against a secure database for user authentication.
(3) Connecting to a payment gateway API securely to process a credit card transaction.

Which of the following are advantages of compiled programs over interpreted programs?

(1) They generally execute faster because the source code has been translated into machine code beforehand.
(2) They are easier to debug during runtime as errors are caught and shown line by line.
(3) The source code does not need to be distributed to end-users, protecting intellectual property.

(a) Character representation:

(i) Explain what "parity bit" is and how odd parity is used to detect transmission errors. (2 marks)

(ii) If the character 'A' is represented by ASCII code 65 (denary), write down its 8-bit representation using odd parity as the most significant bit (MSB). (2 marks)

(b) Sound representation:

A continuous sound wave is digitized.

(i) If the sampling rate is 16 kHz and each sample is stored in 12-bit format. Calculate the data size, in kilobytes (KB), of a 10-second mono sound recording without compression. (Show calculation steps, \(1 \text{ KB} = 1024 \text{ bytes}\)). (3 marks)

(ii) State two methods to reduce the file size of the recorded sound, other than applying file compression, and describe the trade-off of each method on sound quality. (3 marks)

Consider the following pseudocode algorithm designed to process an array of integers representing student test marks to find the length of the longest consecutive sequence of passing marks (>= 50).

1 Input: A, an array of N integers indexed from 1 to N
2 max_len = 0
3 current_len = 0
4 For i from 1 to N:
5 If A[i] >= 50 Then
6 current_len = current_len + 1
7 Else
8 If current_len > max_len Then
9 max_len = current_len
10 EndIf
11 current_len = 0
12 EndIf
13 EndFor
14 If current_len > max_len Then
15 [ Blank X ]
16 EndIf
17 Output max_len

(a)(i) Fill in [ Blank X ] in line 15 so that the algorithm correctly outputs the length of the longest consecutive sequence of passing marks. (1 mark)

(ii) Explain why lines 14-16 are necessary. Give a sample array of size 5 where omitting lines 14-16 would lead to an incorrect output. (2 marks)

(b) Trace the algorithm using the input array \(A = [45, 60, 75, 30, 80, 85, 90, 40]\) of size 8. Provide a trace table showing the values of variables `i`, `A[i]`, `current_len`, and `max_len` at the end of each iteration of the For loop. (4 marks)

(c) A student suggests modifying the algorithm to find the start index of the longest consecutive sequence. Describe the additional variables needed and how they should be updated in the pseudocode. (3 marks)

(a) Explain the main roles of the following registers during the execution of a program instruction:

(i) Program Counter (PC) (2 marks)

(ii) Memory Address Register (MAR) (2 marks)

(iii) Instruction Register (IR) / Current Instruction Register (CIR) (2 marks)

(b) A modern computer system uses multi-level cache (L1, L2, L3) between the CPU and the main memory (RAM).

(i) Explain why cache memory is necessary even though RAM size is increasing significantly. (2 marks)

(ii) Describe how the Principle of Locality (either temporal or spatial) justifies the use of cache memory. (2 marks)

A small company is setting up a local area network (LAN) for its office. The network diagram shows:

- A router connected to the Internet.

- A network switch.

- Ten desktop computers connected to the switch.

- A wireless access point (WAP) connected to the switch.

- A network printer connected to the switch.

(a) IP Addressing and Subnetting:

(i) Explain what "private IP address" means and why it cannot be used directly on the Internet. (2 marks)

(ii) State the role of Network Address Translation (NAT) in this office network. (2 marks)

(iii) The network printer is assigned a static IP address, while the office desktops are assigned dynamic IP addresses. State which protocol is responsible for automatically assigning dynamic IP addresses, and explain why the printer should have a static IP address instead. (2 marks)

(b) Wireless Security and Connection:

(i) The office implements WPA3 for its wireless network instead of WEP. Give two security reasons why WEP should not be used. (2 marks)

(ii) A visitor tries to connect a smartphone to the office Wi-Fi but fails, even though the password entered is correct. Suggest two possible reasons related to network configuration or security settings (e.g., MAC address filtering) that could cause this. (2 marks)

A school uses a spreadsheet to manage student participation in extra-curricular activities.

The spreadsheet contains the following columns:

- Column A: Student ID (e.g., S101)

- Column B: Name

- Column C: Class (e.g., 5A, 5B, 5C)

- Column D: Activity Code (e.g., ACT01, ACT02)

- Column E: Base Fee (in HKD)

- Column F: Subsidy Rate (e.g., 0.2 representing 20%)

- Column G: Subsidized Fee (in HKD)

- Column H: Payment Status (either "Paid" or "Pending")

(a) Formulas:

(i) Write a spreadsheet formula for cell G2 to calculate the subsidized fee of the student in row 2. (The subsidized fee is calculated as: Base Fee * (1 - Subsidy Rate).) (1 mark)

(ii) Cell I2 is used to check if a student is eligible for a special bonus. If a student is in Class "5A" and has a "Paid" status, the formula in I2 should display "Yes", otherwise it should display "No". Write down the formula for I2. (2 marks)

(iii) If the school wishes to calculate the total subsidized fees collected (i.e., only for those with payment status "Paid") across rows 2 to 100, write down a formula using a built-in spreadsheet function to achieve this. (2 marks)

(b) Data Validation and Formatting:

(i) The "Subsidy Rate" in Column F must be a decimal value between 0 and 0.5 (inclusive). Describe how to set up a data validation rule for Column F, including the validation criteria and the benefit of doing so. (3 marks)

(ii) The class teacher wants to quickly identify students who have not paid their fees. Suggest a spreadsheet feature that can automatically highlight cells in Column H with a red fill color if their value is "Pending". (2 marks)