Year 10 · Computer Science · Summer 2
Databases and the Year 10 mock · Lesson 4 of 5
Revision: Paper 1 topics 1 to 3
Exam practice1.1 Number systems2.2 Methods of error detection3.1 Computer architecture
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
You will learn to
- Use the command word to decide what kind of answer a question needs.
- Answer a timed section of Paper 1 questions on topics 1 to 3.
- Calculate how long to spend on a question from its marks.
- Evaluate your answers with the mark scheme and update your RAG list.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Success criteria
You have got it when you can say:
- I can say the difference between State, Describe and Explain.
- I can finish a timed section at about 1.4 minutes per mark.
- I can mark my own answers and colour each syllabus point red, amber or green.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Retrieval starter
Questions from before. Write your answers, then show them.
- Last lesson
The data type for 'has paid' (yes or no) is…
A TextB RealC Boolean
C. Boolean
- Last unit
A compiler…
A Only checks spellingB Translates one line at a time, every runC Translates the whole program once into machine code
C. Translates the whole program once into machine code
- Earlier this year
Typing an email address twice to check it is…
A ValidationB VerificationC A trace table
B. Verification
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Key words (1 of 10)
- Bit
- A single binary digit, 0 or 1.
- Nibble
- A group of 4 bits, which matches one hexadecimal digit.
- Byte
- A group of 8 bits.
- Denary
- The base 10 number system we use every day, with digits 0 to 9.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Key words (2 of 10)
- Binary
- The base 2 number system computers use, with digits 0 and 1.
- Hexadecimal
- The base 16 number system, with digits 0 to 9 and A to F, used to write binary in a short form.
- Overflow
- An error when a result is too big to fit in the number of bits available.
- Logical shift
- Moving all the bits left or right, losing bits off one end and filling the other end with 0s.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Key words (3 of 10)
- Two's complement
- A way to store negative numbers, where the leftmost bit has a negative place value (−128 in 8 bits).
- Colour depth
- The number of bits used to store the colour of each pixel.
- Packet
- A small piece of data sent across a network, with a header, payload and trailer.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Key words (4 of 10)
- Packet switching
- Sending each packet separately, possibly by different routes, then reordering them at the destination.
- Interference
- Unwanted outside signals that can corrupt data on the way.
- Parity bit
- An extra bit that makes the number of 1s in a byte odd or even.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Key words (5 of 10)
- Checksum
- A value calculated from a block of data, recalculated by the receiver to check for errors.
- Echo check
- The receiver sends the data back so the sender can compare it with the original.
- Check digit
- A digit calculated from the other digits of a number, used to catch typing errors.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Key words (6 of 10)
- ARQ
- Automatic repeat query: acknowledgements and timeouts make the sender re-send data that is wrong or lost.
- CPU
- The central processing unit, which processes instructions and data by fetching, decoding and executing them.
- Microprocessor
- A CPU made as an integrated circuit on a single chip.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Key words (7 of 10)
- Von Neumann architecture
- A computer design where instructions and data are stored together in the same memory.
- ALU
- Arithmetic logic unit: does calculations and logical comparisons.
- Control unit
- Manages the fetch–decode–execute cycle and sends control signals.
- Register
- A tiny, very fast store inside the CPU that holds one item.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Key words (8 of 10)
- Bus
- A set of parallel wires that carries addresses, data or control signals.
- Cache
- Small, very fast memory in or near the CPU that holds frequently used data and instructions.
- Clock speed
- The number of cycles the CPU does each second, measured in hertz.
- Core
- A complete processing unit; a multi-core CPU can process several instructions at once.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Key words (9 of 10)
- Instruction set
- The list of all the instructions a particular CPU can carry out.
- Embedded system
- A computer system inside a larger device that does one dedicated job.
- Sensor
- An input device that measures a physical property and sends the reading to a computer.
- NIC
- Network interface card: the hardware that connects a device to a network.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Key words (10 of 10)
- MAC address
- A unique 48-bit address given to a NIC at manufacture, written in hex.
- IP address
- An address given to a device on a network so data can be sent to it.
The explanation · step 1 of 33 · part 1 of 3
Command words: what the question wants
Every exam question starts with a command word. It tells you what kind of answer earns the marks.
The explanation · step 1 of 33 · part 2 of 3
Command words: what the question wants (continued)
| Command word | What it asks for | Example |
|---|---|---|
| State or Give | A short fact. No reason needed. | State one register in the CPU. The MAR. |
| Identify | Name or pick out one thing. | Identify the register that holds the next address. The PC. |
| Define | The exact meaning of a term. | A bit is one binary digit: 0 or 1. |
| Describe | What something is like, or what happens, in order. | The file is split into packets. Each packet may take a different route. |
| Explain | Why or how. Give a reason, joined with 'because' or 'so'. | Hex is shorter than binary, so there are fewer mistakes when reading it. |
| Compare | How two things are alike or different. Mention both things in each point. | Serial sends one bit at a time, but parallel sends several bits at once. |
| Calculate | Work out a number. Show the working and the units. | 800 × 600 × 24 = 11 520 000 bits |
| Evaluate | Judge how good something is. Give points for and against, then a conclusion. | Cloud storage: access anywhere, but needs the internet. Overall … |
| Suggest | Use what you know in a new situation. Several answers can be right. | Suggest a sensor for a car park: infra-red. |
The explanation · step 1 of 33 · part 3 of 3
Command words: what the question wants (continued)
As a rough guide, one mark needs one clear, separate point. A 4-mark question needs about four.
'Describe' does not ask for reasons. 'Explain' does. A description given for an 'explain' question often loses marks.
The explanation · step 2 of 33 · part 1 of 2
Marks per minute
Paper 1 (Computer Systems) lasts 1 hour 45 minutes. It has 75 marks.
105 minutes ÷ 75 marks = 1.4 minutes per mark. Use this to plan each question.
| Marks for the question | Working | Time to spend |
|---|---|---|
| 2 | 2 × 1.4 = 2.8 | about 3 minutes |
| 4 | 4 × 1.4 = 5.6 | about 6 minutes |
| 6 | 6 × 1.4 = 8.4 | about 8 minutes |
The explanation · step 2 of 33 · part 2 of 2
Marks per minute (continued)
Stuck? Leave a gap, mark the question number, and move on. Come back at the end.
Check the paper length on the current Cambridge 0478 syllabus for the year your pupils sit the exam.
The explanation · step 3 of 33 · part 1 of 2
Mark it, then RAG it
A RAG list is the syllabus written as a checklist. Pupils colour each point red, amber or green.
| Colour | It means | What to do next |
|---|---|---|
| Red | I cannot do this yet. | Revise it first. Ask for help. |
| Amber | I can do it, but I make mistakes. | Practise past-paper questions on it. |
| Green | I can do it under time. | Keep it fresh with a short quiz. |
The explanation · step 3 of 33 · part 2 of 2
Mark it, then RAG it (continued)
- Do the timed section in silence.
- Mark it with the real mark scheme.
- Write each missing point in a different colour.
- Update the RAG list from the marks, not from feelings.
- Revise the reds first.
Why mark with the real mark scheme?
It shows the exact points that earn marks. Pupils see what a full answer looks like.
1.1 Number systems · The explanation · step 4 of 33 · part 1 of 2
Why computers use binary
A computer is made of billions of tiny switches called transistors. Each switch is either off or on.
We write off as 0 and on as 1. A number system with only two digits is called binary.
One binary digit is a bit. Eight bits together make a byte.
Every extra bit doubles the number of different patterns you can make.
1.1 Number systems · The explanation · step 4 of 33 · part 2 of 2
Why computers use binary (continued)
Two states are very reliable. A switch is clearly on or clearly off, so the computer rarely misreads a value.
1.1 Number systems · The explanation · step 4 of 33
The maths: How many patterns can n bits make?
1.1 Number systems · The explanation · step 6 of 33 · part 1 of 2
Denary to binary
Start at the left column, 128. Ask: does 128 fit into my number?
If it fits, write 1 and take 128 away. If it does not fit, write 0.
Move to the next column and repeat with what is left. Stop when you reach the 1 column.
Always write all 8 bits, including the 0s at the front.
1.1 Number systems · The explanation · step 6 of 33 · part 2 of 2
Denary to binary (continued)
Each column is used once at most, so taking away the biggest column first always gives the right pattern.
The explanation · 28 more steps
More on the lesson page
The lesson page has the rest of the explanation, step by step:
- Place value: denary and binary
- The biggest number n bits can hold
- Hexadecimal: base 16
- Hex to denary and denary to hex
- Binary and hex using nibbles
- Why hexadecimal is used
- Adding binary: the four rules
- A full 8-bit addition
- Overflow
- Logical left shift
- Logical right shift
- Two's complement: negative numbers
- Denary to two's complement
- Why errors happen
- Parity check: odd and even
- Parity byte and parity block
- Checksum
- Echo check
- Check digits
- Automatic repeat query (ARQ)
- The CPU and the microprocessor
- Von Neumann architecture
- The five registers
- The three buses
- The fetch–decode–execute cycle
- The instruction set
- Cores, cache and clock speed
- Embedded systems
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Quick quiz · 1 of 3
17 MOD 5 is…
- A 2
- B 3
- C 3.4
A. 2
MOD is the remainder: 17 = 3 × 5 + 2. DIV would give 3.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Quick quiz · 2 of 3
A function differs from a procedure because it…
- A Has a name
- B Can have parameters
- C Returns a value
C. Returns a value
Both have names and parameters. Only a function gives a value back.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Quick quiz · 3 of 3
A local variable…
- A Exists only inside its subroutine
- B Never changes
- C Can be used anywhere
A. Exists only inside its subroutine
It is created when the subroutine starts and gone when it ends.
Year 10 · Computer Science · Databases and the Year 10 mock · Lesson 4 of 5
Exit ticket
Answer on paper before you go. Then check.
DECLARE Marks : ARRAY[1:30] OF INTEGER makes…
A 30 whole-number slots, numbered 1 to 30B 30 stringsC One number
A. 30 whole-number slots, numbered 1 to 30 Cambridge arrays start at 1 unless the question says otherwise.
SUBSTRING("Computer", 1, 3) gives…
A ComputerB ComC omp
B. Com Start at position 1, take 3 characters. Cambridge strings start at 1.