DSE ICT Practice Paper: Computer Systems, Networks And Data

DSE ICT Practice Paper: Computer Systems, Networks and Data

2026-11-03

DSE ICT – Systems and Data Practice

DSE ICT practice paper: 12 questions, 100 marks, 75 minutes, covering binary conversion, bitmap and audio file size, transfer time, operating systems, SQL,

Download　Question paper PDF　|　Answer key PDF

Paper details　DSE ICT, binary, file size, SQL, network security, binary search, 12 questions, 100 marks

Section A (Questions 1 to 4, 26 marks)

Read each question and write the correct answer with an explanation. Show working and units for any calculation.

#	Question	Answer and marking notes
1	Convert the binary number 10110110 to decimal and to hexadecimal, and explain why computers use binary rather than decimal.	Reading 10110110 from the left, the place values are 128, 64, 32, 16, 8, 4, 2 and 1. Adding the positions holding a one gives 128 plus 32 plus 16 plus 4 plus 2, which is 182, so the decimal value is 182. Grouping the bits in fours, 1011 is B and 0110 is 6, so the hexadecimal value is B6. Computers use binary because a digital circuit has only two reliable states, high and low voltage, or on and off; representing zero and one with two states is the most reliable and the most immune to noise, and the circuitry is far simpler. Decimal would need ten clearly distinguishable voltage levels, which are much easier to misread.
2	An uncompressed bitmap is 1024 by 768 pixels with 24 bit colour. Find its file size in megabytes, taking 1 MB as 1,048,576 bytes.	The number of pixels is 1024 times 768, which is 786,432. At 24 bits per pixel, that is 3 bytes per pixel, so the total is 786,432 times 3, which is 2,359,296 bytes. Dividing by 1,048,576 gives 2.25 MB. That is the raw uncompressed size; in practice a format such as JPEG is used to reduce storage.
3	Uncompressed stereo audio is sampled at 44,100 Hz with 16 bit samples for 60 seconds. Find its file size in megabytes.	Bytes per second is 44,100 times 2 bytes for a 16 bit sample times 2 channels for stereo, which is 176,400 bytes. Over 60 seconds the total is 176,400 times 60, which is 10,584,000 bytes. Dividing by 1,048,576 gives 10.09 MB. Uncompressed audio is therefore very large, which is why lossy formats such as MP3 are commonly used.
4	A 12 MB file is sent over an 8 Mbps link, taking 1 MB as 8 Mbit. Find the minimum transfer time and explain why the actual time is usually longer.	A 12 MB file is 12 times 8, which is 96 Mbit. The minimum transfer time is 96 Mbit divided by 8 Mbps, which is 12 seconds. The actual time is usually longer because bandwidth is a theoretical maximum: protocol overhead such as headers and acknowledgements, network congestion, server processing and disk access all take time, and the quoted 8 Mbps is normally a download speed while the upload speed may be much lower.

Section B (Questions 5 to 8, 32 marks)

Answer the following questions with working, units and evidence drawn from the data given.

#	Question	Answer and marking notes
5	State four main functions of an operating system, and explain how virtual memory works and give one disadvantage.	Four main functions of an operating system are processor management, which schedules and allocates CPU time; memory management, which allocates and reclaims main memory; file management, which organises directories and controls read and write permissions; and input and output or device management, which drives peripherals through device drivers. It also provides the user interface. Virtual memory treats part of the hard disk as an extension of memory: when main memory runs short, pages not currently in use are moved to a swap file on disk and paged back when needed. The disadvantage is that disk access is far slower than memory, so heavy paging causes thrashing, in which the disk is constantly reading and writing and the system slows markedly; repeated writes also shorten the life of a solid state drive.
6	Explain the difference between a primary key and a foreign key, and write an SQL statement that lists the names of students scoring above 80, highest score first.	A primary key uniquely identifies each row of a table and cannot repeat or be null, for example a student number. A foreign key is a primary key of another table used to link the two tables, for example the student number in a results table, whose value must exist in the student table. The query is: SELECT name FROM student WHERE score > 80 ORDER BY score DESC; The WHERE clause filters the rows and ORDER BY with DESC sorts the result from highest to lowest.
7	Cell C2 contains the formula =A2*B2. What does the formula become when copied to D3, and how should it be rewritten to keep referring to a tax rate held in B2? Explain the difference between relative and absolute references.	Copying from C2 to D3 moves the column one place right and the row one place down, so the formula becomes =B3*C3. To keep referring to the tax rate in B2 the reference must be made absolute by locking its column and its row, so the formula still points at B2 after copying. Relative references adjust automatically with the copy position and suit row by row calculations, whereas absolute references pin a column or row and suit fixed constants such as a tax rate.
8	State three common network security threats and one defence against each.	Three common threats and their defences: (1) phishing email, which impersonates an organisation to obtain passwords; defences include staff awareness training, mail filtering and two factor authentication. (2) malware such as viruses and ransomware, often arriving in attachments or cracked software; defences include antivirus software, prompt patching and regular backups. (3) interception in transit, or a man in the middle attack, capturing data on public Wi-Fi; defences include HTTPS encryption, a virtual private network and avoiding sensitive logins on public networks. No single measure is enough, so layered defence and user vigilance are both required.

Section C (Questions 9 to 12, 42 marks)

Write fuller answers using correct subject terms and support them with examples from Hong Kong or daily life.

#	Question	Answer and marking notes
9	In 1,024 records already sorted by key, what is the maximum number of comparisons for a binary search, and the average number for a linear search? Explain the difference.	A binary search halves the search range at each step, so the number of comparisons is log base 2 of 1,024, which is 10; at most ten comparisons settle the result. A linear search compares items one by one and on average inspects about half the list, that is 512 comparisons, with 1,024 in the worst case. The difference arises because a binary search exploits the fact that the data are sorted, so each comparison discards half the candidates, giving logarithmic time, whereas a linear search needs no sorting but takes linear time. The gap grows enormously with data size, though a binary search first requires sorting and random access.
10	Trace the following code and state the output, explaining the accumulation at each pass: total starts at 0; for i from 1 to 5, if i divided by 2 leaves remainder 0 then total becomes total plus i times i.	The output is 20. The loop runs i from 1 to 5: at i equal to 1 the remainder on division by 2 is 1, so nothing is added; at i equal to 2 the remainder is 0, so total becomes 0 plus 4, which is 4; at i equal to 3 the remainder is 1 and nothing is added; at i equal to 4 the remainder is 0, so total becomes 4 plus 16, which is 20; at i equal to 5 nothing is added. Only the squares of 2 and 4 are summed, giving 20, which shows how a condition can filter out unneeded data.
11	The ASCII value of A is 65 and of a is 97. Find the ASCII value of H and its eight bit binary form, then compare lossless and lossy compression with one example of each.	H is the seventh letter after A, so its ASCII value is 65 plus 7, which is 72. In eight bit binary, 72 is 01001000, that is 64 plus 8. Lossless compression allows the original data to be restored exactly, for example ZIP or PNG, and suits text, source code and any file needing exact recovery. Lossy compression discards some detail in exchange for a much smaller file, for example JPEG or MP3, so the restored data differs from the original, although the difference is usually imperceptible to the eye or ear. The choice depends on how much distortion the data can tolerate.
12	List the five stages of the system development life cycle, explain the difference between unit testing and system testing, and state two benefits and one risk of cloud computing.	The five stages of the system development life cycle are requirements analysis, system design, implementation or programming, testing, and deployment with maintenance. Unit testing is carried out by programmers on a single function or module to check that its logic is correct, whereas system testing integrates the modules and tests the whole system, checking interfaces between modules, data flow and whether the running system meets the requirements. Benefits of cloud computing are pay as you go, which avoids heavy upfront hardware spending, and elastic scaling to meet peak demand; a risk is that data sit with a third party, so an outage or a compromised account can make data unavailable or exposed, which is why encryption and backups matter.

Find a tutor — free Tutor Registration →

A TutorZone practice paper; original questions and passages, not publisher material.