Paper 1: Theory Fundamentals (Cambridge (CIE) A Level Computer Science): Revision Note

Paper 1 overview

What is in 9618 Paper 1?

• Paper 1 Theory Fundamentals is a 1 hour 30 minute written paper worth 75 marks

• It is 50% of the AS Level and 25% of the A Level

• It covers syllabus sections 1 to 8:

  • information representation

  • communication

  • hardware

  • processor fundamentals

  • system software

  • security, privacy and data integrity

  • ethics and ownership

  • databases

• You answer all questions; there is no choice

• Calculators are not allowed, so every conversion and file size calculation is done by hand

• Questions range from 1-mark recall to longer answers set in a scenario, such as a company, a device or a network

• For advice that applies to every 9618 paper, see:

  • CIE A Level Computer Science exam tips

  • 9618 command words

Question types and how to answer them

How do you answer number conversion questions?

• Typical stems include:

  • "Convert the denary number 241 to hexadecimal"

  • "Convert the two's complement binary number into denary"

  • "Subtract the denary number 10 from the denary number 100 using binary subtraction. Show your working."

• Check which representation the question gives you before you start

  • Examiners reported a very common wrong answer where students treated an unsigned binary integer as Binary Coded Decimal (BCD) and converted it directly

  • Another common error was converting a binary integer into denary when the question asked for hexadecimal

• If the question says "using binary subtraction" (or binary addition), the working must be in binary

  • Examiners give no credit for doing the calculation in denary and converting the answer to binary

  • Watch the order: 100 − 10 is not the same as 10 − 100, and examiners report this being reversed

How do you answer file size calculations?

• Typical stems include:

  • "Calculate the file size of a bitmap image... Give your answer in kibibytes. Show your working."

  • "Calculate the file size of the recording. Give your answer in megabytes and show your working."

• Mark schemes usually award 1 mark for the working and 1 mark for the answer

• Follow three steps:

  • Multiply the values given (for an image: width × height × bit depth)

  • Divide by 8 if the bit depth is in bits and the answer is in bytes; examiners report that a frequent wrong answer missed this division

  • Divide by 1000 or 1024 for each step up in units, depending on which unit the question asks for

• Check the unit the question asks for, as the decimal and binary prefixes are different

• Examiners also report students confusing these units, for example swapping kibibytes and kilobytes

• Without a calculator, choose an order of working that keeps the numbers simple; for example, divide by 8 and by 1024 early when the values are powers of 2

How do you answer bit depth, resolution and sampling questions?

• These questions usually ask about the effect of a change, not the definition

• Say clearly whether the value increases or decreases, then describe the effect on the image or the sound

• Examiners report that many answers about changing bit depth only talked about file size when the question asked how the image is affected

• Restating the definition ("increasing the bit depth increases the number of bits per pixel") is not enough; say what changes for the user, such as more colours being available

How do you answer logic gate and truth table questions?

• Typical stems include "Draw the logic circuit for the logic expression" and "Complete the truth table for the logic expression"

• Draw each gate with the correct shape

  • Examiners report that OR and AND gates were often hard to tell apart, and that NOT gates were drawn without the circle

• Draw the circuit exactly as the expression is written

  • Examiners report missing NOT gates, and students replacing (NOT R) OR (NOT M) with a single NOR gate, which is a different expression

• In a truth table, list the inputs in binary counting order (000, 001, 010...) so that no row is missed

How do you answer questions set in a scenario?

• Many Paper 1 questions describe a situation, such as a video doorbell, a laser printer or a company network, then ask you to describe or explain something about it

• Every point should link to the scenario; a textbook definition on its own often scores nothing

• For 2-mark questions, give two different points; examiners report answers where the same point was written twice in different words. If the answer space is numbered, only the first answer in each space is marked

• Read the scenario details carefully, as they often tell you which answer is expected (for example, a question about a bitmap image needs an answer about pixels and colours, not about text characters)

How do you answer ethics and ownership questions?

• Typical stems include "Explain the reasons why the computer programmer needs to act ethically towards colleagues" and "Explain why it is important for a programmer to join a professional ethical body"

• Learn what a professional ethical body is (the syllabus names the British Computer Society (BCS) and the Institute of Electrical and Electronic Engineers (IEEE)); examiners report students thinking it was an employer or part of the company

• When a scenario describes someone acting unethically, explain why their action was unethical; examiners report that answers only saying what the person should have done did not answer the question

How do you answer assembly language trace questions?

• Typical stems ask you to complete a trace table showing the contents of the Accumulator (ACC), the Index Register (IX) and memory as each instruction runs

• Work through one instruction at a time and update only the register or memory location that the instruction changes

• Examiners report three common errors:

  • Indexed addressing is often misunderstood; for example, LDX 110 was wrongly treated as loading the value 110 into the accumulator

  • Storing a value from the accumulator copies it; the accumulator is not reset to zero

  • Output values are written without quotation marks; otherwise correct trace tables lost marks for putting the output in quotation marks

How do you answer SQL questions?

• Typical stems include "Write a Structured Query Language (SQL) script to..." and "Write a Data Definition Language (DDL) script to..."

• Copy table and attribute names exactly as the question gives them; examiners report marks lost when these were copied wrongly

• If a question asks you to identify and correct errors in an SQL script, write the corrected statement as well as naming the error; examiners report answers that found the errors but gave no correction

• Use SQL data types such as VARCHAR(n), INTEGER and DATE, not data types from a programming language

• Put quotation marks around text values but not around Boolean or numeric values, and use the SQL functions in the syllabus, such as AVG, SUM and COUNT; examiners report marks lost for quotation marks around a Boolean value in a WHERE clause

• Examiners report that the primary and foreign key clauses are often the hardest part, so learn PRIMARY KEY (Field) and FOREIGN KEY (Field) REFERENCES Table (Field)

Common mistakes in Paper 1

• Answering in denary when the question asks for hexadecimal, or the other way round

• Leaving out the "divide by 8" step in file size calculations

• Not stating whether a value goes up or down when describing the effect of a change

• Replacing a combination of gates with a single NOR gate, which changes the expression

• Writing the same point twice in different words for a 2-mark question