IGCSE Computer Science 0478 Paper 1 Practice Paper | 30 questions, 75 marks, 1 h 45 min

2026-10-31

IGCSE Computer Science 0478 Paper 1

IGCSE Computer Science 0478 Paper 1: 30 questions, 75 marks, 1 h 45 min, covering binary, file size, compression, networks, security, algorithms and databases, with answer PDF.

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Paper details　Level: IGCSE Year 10-11 | Subject: Computer Science 0478 | Time: 1 hour 45 minutes | Marks: 75 | Questions: 30

Section A — Data representation, hardware and software (32 marks)

Show all working. Method marks are not awarded for answers alone.

#	Question	Answer and marking notes
1	Convert the denary number 205 into 8-bit binary and give its hexadecimal value. (2 marks)	205 = 128 + 64 + 8 + 4 + 1, so 11001101; hexadecimal CD.
2	Convert the binary number 10110110 into denary and give its hexadecimal value. (2 marks)	10110110 = 128 + 32 + 16 + 4 + 2 = 182; in two groups of four bits, 1011 0110 gives B6.
3	Represent −45 in 8-bit two’s complement and state the role of the most significant bit. (3 marks)	45 = 00101101; invert to 11010010 and add 1 to get 11010011 (denary 211, hex D3). A most significant bit of 1 means the value is negative.
4	An image is 1024 × 768 pixels with a colour depth of 24 bits. Calculate its file size in KiB (1 KiB = 1024 bytes). (3 marks)	1024 × 768 × 24 ÷ 8 = 2359296 bytes, ÷ 1024 = 2304 KiB.
5	If the colour depth of that image is reduced to 8 bits, what is the new file size in KiB and the percentage saved? (3 marks)	1024 × 768 × 8 ÷ 8 = 786432 bytes = 768 KiB; saving (2304 − 768) ÷ 2304 = 66.7 per cent.
6	A 30-second stereo recording is made at 44.1 kHz with a sample resolution of 16 bits. Calculate its size in MiB (1 MiB = 1048576 bytes). (3 marks)	44100 × 16 × 2 × 30 ÷ 8 = 5292000 bytes, ÷ 1048576 ≈ 5.05 MiB.
7	The recording from the previous question is downloaded over a 10 Mbit/s connection. Calculate the time needed in seconds. (2 marks)	5292000 × 8 = 42336000 bits, ÷ 10000000 = 4.23 seconds.
8	A system uses even parity. Seven data bits 1011001 are transmitted. State the parity bit and explain why this check cannot detect two bits being corrupted at the same time. (3 marks)	The data contain four 1s, already even, so the parity bit is 0 (10110010 is sent). If two bits flip, the number of 1s is still even and the check still passes.
9	Run-length encoding (RLE) is applied to the string AAAABBBCCD. Write the encoded result and state the percentage saved. (3 marks)	4A3B2C1D, which is 8 characters; the original has 10 characters, a saving of 20 per cent.
10	State one main difference between RAM and ROM. (2 marks)	RAM can be read and written and loses its contents when power is removed; ROM is normally read only and keeps its contents, so it stores the start-up program.
11	Explain how cache memory speeds up the execution of a program. (3 marks)	Cache is small, very fast memory inside the CPU that holds recently or frequently used instructions and data; reading from cache is much faster than reading from main memory, so the CPU waits less.
12	Computer A has one 3.5 GHz core; computer B has four 2.0 GHz cores. Explain why B is not necessarily faster than A. (3 marks)	B has a lower clock speed, so each instruction takes more clock cycles; extra cores only help when the program can be split into threads that run in parallel; a program that must run in sequence may run faster on A; cache size, RAM and bus speed also matter.

Section B — Networks, network security and the cloud (24 marks)

Answer in full sentences.

#	Question	Answer and marking notes
13	A MAC address is 48 bits long. How many bytes is that, and how does a MAC address differ from an IP address? (2 marks)	48 ÷ 8 = 6 bytes. A MAC address is fixed in the network interface by the manufacturer and identifies a device within the same network; an IP address is assigned by the network for routing between networks and can change.
14	Explain the different roles of a switch and a router in a network. (3 marks)	A switch forwards frames to a particular device inside a LAN using MAC addresses; a router forwards packets between different networks using IP addresses and connects the LAN to the internet.
15	Explain why a message is split into packets before transmission. (2 marks)	Packets can travel independently along different routes and use several links at once; if a packet is corrupted only that packet is resent; it also stops one message from occupying a link for a long time.
16	A 30 MiB file is sent in packets that each carry a 1500-byte payload. How many packets are needed? (1 MiB = 1048576 bytes; the last packet may be partly filled) (3 marks)	30 × 1048576 = 31457280 bytes; 31457280 ÷ 1500 = 20971.52, so 20972 packets are needed.
17	Compare symmetric and asymmetric encryption and give one use of each. (2 marks)	Symmetric encryption uses the same key to encrypt and decrypt, is fast and suits bulk data such as the traffic inside an HTTPS session; asymmetric encryption uses a public and a private key, and is used to exchange keys and to create digital signatures.
18	State two features that help you recognise a phishing email. (2 marks)	The sender domain does not match the official organisation or is misspelt; the message urges the reader to click a link and enter a password or personal data; or an attachment asks for macros to be enabled.
19	How does a firewall differ from a proxy server in protecting a network? (3 marks)	A firewall sits at the network boundary and blocks or allows traffic by rules; a proxy server makes requests to the internet on behalf of internal users, hides their IP addresses, and can filter and cache web pages.
20	Explain the difference between two-factor authentication (2FA) and biometric authentication, giving one example of each. (2 marks)	2FA requires two different types of credential, such as a password plus a code sent by text message; biometric authentication uses a body feature such as a fingerprint or a face, which is a single type of factor.
21	Explain why HTTPS is more secure than HTTP. (2 marks)	HTTPS runs HTTP over TLS, so the traffic is encrypted and the server is identified by a certificate, which prevents eavesdropping and man-in-the-middle attacks.
22	Give three benefits of cloud storage for a school and one risk. (3 marks)	Benefits: files can be reached from anywhere; automatic backup and version history; capacity grows on demand without the school running its own server. Risk: the school depends on the internet and the provider, and the data sits with a third party, possibly abroad, so privacy and contract terms must be checked.

Section C — Algorithms, programming and databases (19 marks)

Use integer indexes in pseudocode; end SQL statements with a semicolon.

#	Question	Answer and marking notes
23	A binary search is used on 15 sorted items. What is the maximum number of comparisons needed, and why? (3 marks)	Each comparison halves the range: 15 → 7 → 3 → 1, so at most 4 comparisons; since 2 to the power 4 is 16, which is not less than 15, the answer is ceil(log2 16) = 4.
24	If a linear search were used instead, how many comparisons are needed in the worst case? (1 mark)	15 comparisons (the item is last or not in the list, so every item is checked).
25	Explain why a binary search must be used on sorted data. (2 marks)	A binary search decides from a comparison of values which half to discard; if the data are not sorted, the discarded half may still contain the target and the result is wrong.
26	Write pseudocode that finds the largest value in the array scores, which holds 20 integers. (3 marks)	max ← scores[1]; FOR i ← 2 TO 20; IF scores[i] is greater than max THEN max ← scores[i]; ENDIF; NEXT i; OUTPUT max. (Equivalent code accepted: initial value, loop range, comparison and output each carry marks.)
27	Trace the following code and state the output: total ← 0; FOR i ← 1 TO 5; total ← total + i * 2; NEXT i; OUTPUT total (3 marks)	i runs from 1 to 5, adding 2 + 4 + 6 + 8 + 10 = 30, so the output is 30.
28	Explain the purpose of a primary key in a database. (2 marks)	A primary key uniquely identifies each record, cannot repeat and cannot be empty (for example StudentID); it links tables and prevents duplicate records.
29	The table Students(StudentID, StudentName, Form, House) exists. Write SQL to list the names of students in form 4A, sorted by name. (3 marks)	SELECT StudentName FROM Students WHERE Form = ‘4A’ ORDER BY StudentName;
30	Explain the difference between validation and verification of data. (2 marks)	Validation checks that input follows rules such as a range check or a format check, so the data are sensible; verification checks that the data match the original source, for example by double entry or checking a document, so they were copied correctly.

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