MskProdComputing

OCR J277 GCSE Computer Science · 1.2 Memory and Storage

Stretch tasks Units of Data

Task 1

Quiz Challenge

A quiz game against four computer players, then short and long written answers.

  1. Quiz Blitz12 questions against the clock
  2. Quick Fire4 short answers
  3. Big Think2 long answers

About 20 minutes

Task 2

This or That

Pixel the cat asks 8 questions. Each has two answers: pick the right one.

  • Two answers to every question
  • A fish treat for every right answer
  • Streaks win Pixel shades, then a party hat

About 4 minutes

Task 3

Memory Match

Flip the cards two at a time to match each unit card to its size card.

  • 12 cards: each unit has a size
  • One peek at every card
  • Combo points for pairs found in a row

6 pairs, about 4 minutes

Task 4

Sort It

Sort each statement into the right box, like the tick-box tables in the exam.

  • 12 cards to sort into 3 boxes
  • Drag a card, tap a box or press its number
  • Combo points for cards sorted in a row

12 cards, about 4 minutes

The games need JavaScript. Every question is below, with the answers at the end.

Read the lesson: Units of Data

Units of Data: the questions

Quiz Challenge, round 1: Quiz Blitz

  1. How many bits are in a byte?

    • 8
    • 4
    • 16
    • 1000

  2. Why do computers use binary?

    • Binary is easier for people to read
    • Denary cannot store text
    • Their components have two reliable states
    • Binary numbers are shorter

  3. How many bytes are in 3 KB? Use 1000, as OCR does.

  4. Order these units from smallest to largest.

    Number these 1 to 6.

    • Nibble
    • Byte
    • Kilobyte
    • Megabyte
    • Gigabyte
    • Bit

  5. OCR J277 uses 1024 bytes in a kilobyte.

    • True
    • False

  6. What is 2.5 GB in MB?

    • 2.5 MB
    • 2,500 MB
    • 250 MB
    • 25,000 MB

  7. A 200 character message uses 8 bits per character. How many bytes is it?

  8. Which formula gives an image's file size in bits?

    • Colour depth x height x width
    • Height x width only
    • Colour depth x number of colours
    • Height + width + colour depth

  9. Which formula gives a sound file's size in bits?

    • Sample rate x duration x bit depth
    • Sample rate x bit depth
    • Duration x number of speakers
    • Sample rate + duration + bit depth

  10. An image is 100 x 50 pixels with a colour depth of 8 bits. How many bytes is it?

  11. A nibble is half a byte.

    • True
    • False

  12. How many bits are in 2 KB?

    • 16,000
    • 2,000
    • 16,384
    • 256

Quiz Challenge, round 2: Quick Fire

  1. Explain why computers use binary. [2 marks]

  2. Calculate the size in bytes of a 250 character message stored in ASCII using 7 bits per character. Show your working. [2 marks]

  3. Convert 4,500,000 bytes into megabytes. Show your working. [2 marks]

  4. State what is meant by colour depth. [2 marks]

Quiz Challenge, round 3: Big Think

  1. An image is 1000 pixels wide and 800 pixels high, with a colour depth of 24 bits. Calculate its file size in megabytes. Show your working. [4 marks]

  2. A 30 second sound clip is recorded at a sample rate of 44,100 Hz with a bit depth of 16 bits. Calculate its size in kilobytes. Show your working. [4 marks]

This or That: tick the right answer

  1. Which is bigger?

    • 900 MB
    • 1 GB

  2. How many different values can one bit represent?

    • 8
    • 2

  3. To turn bytes into kilobytes, you...

    • Multiply by 1000
    • Divide by 1000

  4. To turn bytes into bits, you...

    • Divide by 8
    • Multiply by 8

  5. What is 6,000 bytes in kilobytes?

    • 60 KB
    • 6 KB

  6. An answer must be in kilobytes, but you leave it in bits. What happens?

    • You lose the mark
    • You still get full marks

  7. Which is smaller?

    • A nibble
    • A byte

  8. How many colours can a colour depth of 8 bits show?

    • 8
    • 256

Memory Match: match each unit to its size

UnitSize
A Bit1 1000 kilobytes
B Nibble2 A single 1 or 0
C Byte3 4 bits
D Kilobyte4 1000 gigabytes
E Megabyte5 8 bits
F Terabyte6 1000 bytes

Sort It: tick one box in each row

Is each amount smaller than, exactly or bigger than 1 MB? Use 1000, as OCR does.

StatementSmaller than 1 MBExactly 1 MBBigger than 1 MB
500,000 bytes
0.5 GB
2,000 KB
1 GB
80,000 bits
4,000,000 bits
1,000,000 bytes
0.001 GB
1000 KB
999 KB
8,000,000 bits
1 TB
Answers

Round 1: Quiz Blitz

  1. 8 A byte is 8 bits. Half a byte, 4 bits, is a nibble.
  2. Their components have two reliable states A transistor is on or off, so two states can be told apart quickly and reliably.
  3. 3000 1 KB is 1000 bytes, so 3 KB is 3000 bytes.
  4. Bit → Nibble → Byte → Kilobyte → Megabyte → Gigabyte 1 bit, 4 bits, 8 bits, then each unit is 1000 of the one before.
  5. False OCR uses 1000. A question will say so if it wants 1024.
  6. 2,500 MB Going down a unit, multiply by 1000: 2.5 x 1000 = 2,500 MB.
  7. 200 200 x 8 = 1600 bits, and 1600 / 8 = 200 bytes.
  8. Colour depth x height x width Every pixel needs colour-depth bits, and there are height x width pixels.
  9. Sample rate x duration x bit depth Samples per second, times seconds, times the bits in each sample.
  10. 5000 8 x 100 x 50 = 40,000 bits, and 40,000 / 8 = 5,000 bytes.
  11. True A nibble is 4 bits and a byte is 8.
  12. 16,000 2 KB is 2,000 bytes, and 2,000 x 8 = 16,000 bits.

Round 2: Quick Fire

    • Their components have two states, on and off
    • Two states can reliably stand for 1 and 0
    Model answer

    Computers are built from components such as transistors that have two states, on and off. Two states can be told apart reliably, so they represent 1 and 0.

    • 250 x 7 = 1750 bits
    • 1750 / 8 = 218.75 bytes
    Model answer

    250 x 7 = 1750 bits. 1750 / 8 = 218.75 bytes.

    • Divide by 1000 twice, or by 1,000,000
    • 4.5 MB
    Model answer

    4,500,000 bytes divided by 1000 is 4500 KB, and 4500 KB divided by 1000 is 4.5 MB.

    • The number of bits
    • Used to store the colour of each pixel
    Model answer

    Colour depth is the number of bits used to store the colour of each pixel.

Round 3: Big Think

    • 24 x 1000 x 800 = 19,200,000 bits
    • Divide by 8: 2,400,000 bytes
    • Divide by 1000: 2400 KB
    • Divide by 1000: 2.4 MB
    Model answer

    24 x 1000 x 800 = 19,200,000 bits. 19,200,000 / 8 = 2,400,000 bytes. 2,400,000 / 1000 = 2400 KB. 2400 / 1000 = 2.4 MB.

    • Uses sample rate x duration x bit depth
    • = 21,168,000 bits
    • Divide by 8: 2,646,000 bytes
    • Divide by 1000: 2646 KB
    Model answer

    Size in bits = sample rate x duration x bit depth = 44,100 x 30 x 16 = 21,168,000 bits. 21,168,000 / 8 = 2,646,000 bytes. 2,646,000 / 1000 = 2646 KB.

This or That

  1. 1 GB 1 GB is 1000 MB, so it beats 900 MB.
  2. 2 A bit is a single 1 or 0, so it has just two possible values.
  3. Divide by 1000 Going up a unit means fewer, bigger units, so divide.
  4. Multiply by 8 Each byte holds 8 bits, so there are 8 times as many bits.
  5. 6 KB 6,000 / 1000 = 6 KB.
  6. You lose the mark Marks are lost on units, not maths: convert to the unit the question asks for.
  7. A nibble A nibble is 4 bits. A byte is 8.
  8. 256 n bits give 2 to the power n colours, and 2 to the power 8 is 256.

Memory Match

  • A 2 Bit: A single 1 or 0
  • B 3 Nibble: 4 bits
  • C 5 Byte: 8 bits
  • D 6 Kilobyte: 1000 bytes
  • E 1 Megabyte: 1000 kilobytes
  • F 4 Terabyte: 1000 gigabytes

Sort It

  1. Smaller than 1 MB 500,000 bytes 500,000 bytes is 500 KB, half a megabyte.
  2. Bigger than 1 MB 0.5 GB 0.5 x 1000 = 500 MB.
  3. Bigger than 1 MB 2,000 KB 2,000 / 1000 = 2 MB.
  4. Bigger than 1 MB 1 GB 1 GB is 1000 MB.
  5. Smaller than 1 MB 80,000 bits 80,000 / 8 = 10,000 bytes, which is just 10 KB.
  6. Smaller than 1 MB 4,000,000 bits 4,000,000 / 8 = 500,000 bytes, which is only 0.5 MB.
  7. Exactly 1 MB 1,000,000 bytes 1000 x 1000 = 1,000,000 bytes, which is 1 MB.
  8. Exactly 1 MB 0.001 GB 0.001 x 1000 = 1 MB.
  9. Exactly 1 MB 1000 KB 1 MB is 1000 KB.
  10. Smaller than 1 MB 999 KB 999 KB is 1 KB short of 1 MB.
  11. Exactly 1 MB 8,000,000 bits 8,000,000 / 8 = 1,000,000 bytes, which is 1 MB.
  12. Bigger than 1 MB 1 TB 1 TB is 1000 GB, which is 1,000,000 MB.