WACE Computer Science: Core Concepts and Exam Technique
What this section covers
WACE Computer Science questions draw on a fixed set of ideas: data representation, hardware and the fetch-execute cycle, networks, algorithms and programming constructs, databases, and the social and ethical dimensions of computing. You must be able to define each term precisely, explain how components interact, and apply a concept to an unfamiliar scenario rather than merely recall a definition.
Concepts you must understand
Be fluent in binary, hexadecimal and two's complement, including overflow and why signed ranges are asymmetric. Know the purpose of registers (program counter, instruction register, accumulator, status flags) and the role of the control unit and ALU. For networks, distinguish LAN from WAN, explain packet switching, and match protocols to layers: IP, TCP and UDP, HTTP/HTTPS, DNS, DHCP. For algorithms, read pseudocode, trace loops and arrays, and state complexity in big-O terms. For databases, explain primary and foreign keys, normalisation to third normal form, and the difference between a query and a view.
Traps that appear in questions
Typical traps include confusing a compiler with an interpreter, treating a stack as FIFO (it is LIFO), claiming that hexadecimal is 'more efficient' in storage rather than simply more compact for humans to read, and mixing up lossy and lossless compression. Another common error is describing encryption as integrity checking; hashing provides integrity, encryption provides confidentiality. Watch for questions asking for a reason rather than a definition.
Rule of thumb and worked example
Rule of thumb: for any 'explain why' question, give the mechanism and then the consequence. Worked example: convert -5 to 8-bit two's complement. Write +5 as 00000101, invert to 11111010, add 1 to get 11111011. State the check: the leading bit is 1, so the value is negative, and 11111011 equals -128 + 123 = -5. Showing the check earns method marks even if the arithmetic slips.
WACE Computer Science: Algorithms, Programming and Problem Solving
What this section covers
This domain tests your ability to design, trace and evaluate algorithms. Questions present pseudocode or a short scenario and ask you to predict output, find a logical error, compare approaches, or justify a data structure. You need working knowledge of sequence, selection and iteration, plus modular design through functions and parameters.
Concepts you must understand
Know the standard algorithms: linear and binary search, bubble, insertion and merge sort, and simple recursion. Be able to state preconditions, such as binary search requiring sorted data. Understand the difference between a syntax error, a logic error and a runtime error, and identify each from a trace. Recognise when to use an array, a list, a record, a stack or a queue. Explain the purpose of test data: normal, boundary and erroneous. Understand why validation (range checks, type checks) differs from verification (double entry, parity).
Traps that appear in questions
Common errors include assuming binary search is always faster regardless of data size, forgetting that it needs sorted input, and miscounting loop iterations by one. Students often confuse a parameter with an argument, or describe a function as returning a value when the pseudocode only prints one. Another trap is describing a logic error as a syntax error because the program still runs; if it runs but gives wrong output, it is a logic error.
Rule of thumb and worked example
Rule of thumb: trace with a table, one column per variable, and write each iteration. Worked example: binary search for 7 in [1, 3, 5, 7, 9, 11]. Low=0, high=5, mid=2 gives 5, which is too small, so low=3. Mid=(3+5) div 2=4 gives 9, too large, so high=3. Mid=3 gives 7: found in three comparisons. Notice that linear search would need four. Compare counts explicitly to earn comparison marks.
WACE Computer Science: Data, Hardware and Systems
What this section covers
This domain examines how data is represented and how hardware executes instructions. Questions ask you to convert between number bases, calculate storage requirements, explain the role of components, and describe how an operating system manages resources.
Concepts you must understand
Be confident with bits, bytes and binary prefixes, and with character encoding such as ASCII and Unicode. Understand how images are stored as pixels with colour depth, how sound is sampled with rate and resolution, and how file size follows from these. Explain the fetch-decode-execute cycle, the role of cache and the difference between RAM and ROM. Distinguish magnetic, optical and solid-state storage, and describe the purpose of an operating system: process scheduling, memory management, file management, device drivers and security.
Traps that appear in questions
Frequent traps include confusing bits with bytes when calculating sizes, using 1000 instead of 1024 for binary prefixes, and forgetting that colour depth multiplies image size. Students often say RAM is 'faster' without explaining volatility or access time, or claim cache stores the operating system permanently. Another trap is describing virtual memory as extra physical RAM; it is disk space used as an extension of memory and is much slower.
Rule of thumb and worked example
Rule of thumb: always write the unit at every step of a calculation. Worked example: an uncompressed image is 800 by 600 pixels at 24-bit colour. Pixels = 480000. Bits = 480000 x 24 = 11520000 bits. Bytes = 11520000 / 8 = 1440000 bytes. In megabytes, 1440000 / 1024 / 1024 is approximately 1.37 MiB. Showing each conversion protects you against a single arithmetic slip, and marks are usually allocated per correct stage.
WACE Computer Science: Networks, Security and Impacts
What this section covers
This domain covers how systems communicate and how their use affects people and society. Questions ask you to describe topologies, explain protocols, identify threats and countermeasures, and discuss legal and ethical issues such as privacy, intellectual property and the digital divide.
Concepts you must understand
Know star versus bus topologies and the roles of switch, router, gateway and firewall. Explain packet switching, IP addressing, DNS resolution and the client-server model. For security, distinguish malware types, phishing and social engineering, and match countermeasures: strong authentication, encryption, access levels, patching and backups. Understand symmetric versus asymmetric encryption and the role of a digital signature. For impacts, prepare balanced arguments about employment, accessibility, environmental cost and data collection.
Traps that appear in questions
Traps include confusing a firewall with antivirus software, claiming HTTPS encrypts the whole path rather than the connection, and describing a switch as routing between networks. Students often present only one side of an ethical issue, or assert that encryption 'stops hacking' rather than protecting confidentiality if data is intercepted. Another trap is treating a backup as a security control against data theft; backups address loss, not unauthorised access.
Rule of thumb and worked example
Rule of thumb: for evaluation questions, use a claim-evidence-impact structure and give both sides. Worked example: 'A school stores student records in the cloud. Discuss one benefit and one risk.' Benefit: staff can access records from any campus, improving continuity when a site is unavailable. Risk: a misconfigured access setting could expose personal data, breaching privacy obligations. Mitigation: role-based access control and encryption at rest. Naming a specific mitigation distinguishes a top-band answer from a general one.