CS04 : Quantifying Data

A detailed look at the collective ways in which computer scientists can group data.  It is required by all examination boards.

https://docs.google.com/presentation/d/1CSI3ZS9gveKYI9dqMFGrS5I4WdXJTFuqExGh2UQ_zMg/preview?slide=id.g3cb6bc7fc1_0_0Learning Outcomes
Quantifying Data

We are learning ...
  • To use the terminology used in engineering and computing to quantify data.
So that we can ...
  • Discuss storage quantities effectively
    - Bit / nybble / byte
    - Kilo / mega / giga / tera / peta
  • Calculate file sizes

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Activity 1
Collective nouns

Humans like to give objects names. We call these nouns. When we want to refer to more than one of the same object, we often refer to the group using a different name. These are called collective nouns. Your teacher might have referred to you as class when you walked into the room for instance.

Task 1.1 A Stress of Worksheets
Where we learn some fun facts about collective nouns

Perform some research

Perform some research into collective nouns on the World Wide Web (HINT : Try Googling 'collective nouns'). 

On the worksheet

Now download and complete worksheet 'Collective Nouns'.

https://docs.google.com/presentation/d/1CSI3ZS9gveKYI9dqMFGrS5I4WdXJTFuqExGh2UQ_zMg/preview?slide=id.g41ede28256_0_8Activity 2
Computing collective nouns

The smallest unit of measurement in a computer system is the bit. Bit stands for Binary Digit. Look carefully at the following popup which describes the relationship between bits, nybbles, bytes and words.

Click to enlarge

Task 2.1 Getting into groups
Where we learn about the basic groupings of data in computer science

As a class

Your teacher will ask you to get into groups of bits, nybbles, bytes and words. You will need to remember these terms during the course.

In your notebooks / on paper

Make some notes from the popup and from the activity you have done in class which will help you to remember the key terms bit, byte, nybble and word.

Where did Bytes Come From? - Computerphile (11:30)

https://docs.google.com/presentation/d/1CSI3ZS9gveKYI9dqMFGrS5I4WdXJTFuqExGh2UQ_zMg/preview?slide=id.g41ede28256_0_20Activity 3
Quantity prefixes

A quantity prefix comes before a basic unit of measure to indicate a multiple or fraction of a unit. In computer maths, science and computer science, we use quantity prefixes to indicate higher multiples or fractions of basic units.

Task 3.1 Worksheet
Where we learn about the metric quantity prefixes

Discuss this popup with your shoulder partner

First, click on the popup and discuss it with your shoulder partner. It shows how we use words to describe quantities. The values in the green rows are the ones which you will hear about most often.

Click to engage

On the worksheet

Now, download and complete the worksheet 'Quantity prefixes'.

Task 3.2 Questions to challenge you
Where we learn how to convert data in one unit into another

In your notebooks

Answer the following questions in full sentences in your notebooks or on paper.
  1. How many bytes (B) in a byte (B)? (Not a trick question - this is the base unit!)
  2. How many bytes (B) in a kilobyte (kB)?
  3. How many bytes (B) in a megabyte (MB)?
  4. How many bytes (B) in a gigabyte (GB)?
  5. How many bytes (B) in a terabyte (TB)?

    Harder questions

  6. How many kilobytes (kB) in a megabyte (MB)?
  7. How many kilobytes (kB) in a gigabyte (GB)?
  8. How many megabytes (MB) in a terabyte (TB)?
  9. How many terabytes (TB) in a petabyte (PB)?

Task 3.3 Fancy a challenge?
Where we learn about binary quantity prefixes

Even though most computer scientists use these 'metric prefixes' to group together bytes, they often don't actually group them powers of 10 (denary). Since computer scientists work in base 2 (binary), they group in powers of 2. We chose the nearest base 2 quantity to the base 10 metric prefix, so, we still use the prefix kilo to mean 1024 when it actually means 1000. Go figure!

1 Kilobyte (kB) = 1000 bytes (B) in metric or 1024 bytes (B) in binary.

We should be using different names for the 'binary prefixes' (and indeed, most computer scientists do). Open up the popup and check out the unusual prefix names. Have you ever seen them before?


Some of the numbers for the larger prefixes are very big - too big for your calculator. However, we can use Python to help - it's also a really good calculator!

This diagram shows you how to perform simple mathematical operations using Python.

Try these examples out in Python before you start the activity.

At the prompt
 / In your notebooks

Use Python as a calculator to work out the answers to the following questions. Write the answers in full sentences in your notebooks.
  1. How many bytes (B) are there in 20 kibibytes (KiB)?
  2. How many bytes (B) are there in 320 gibibytes (GiB)?
  3. How many bytes (B) are there in 1.2 tebibytes (TiB)?
  4. How many kibibytes (KiB) are there in 128 gibibytes (GiB)?
  5. How many gibibytes (GiB) are there in a 256 gigabyte (GB) hard drive? CAREFUL!

This is really important - write it down in your notebooks! Now!

Assessment Task (Homework)

There are a couple of fantastic website resources you can visit to help you understand scale.
In your notebooks, write down 5 interesting facts that you have learnt from these web resources.

Grading rubric

MASTER :  You produce 5 really interesting facts from the websites.  You may even have looked at other websites.
APPRENTICE You produce 3 or 4 fairly interesting facts but you don't really seem to have found them interesting.
NOVICE : You produce less than 3 facts which aren't really interesting.

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Click to load key word list to help you make your own flash cards 

Hungry for more?

Carry out some research into the reasons why quoted hard drive capacity is often less that expected. This website will help. You may want to discuss what you've found out with your computing teacher - they will be impressed!

You may also want to read a little more about the origin of the binary prefix values here.