### How to Pass CIE A Level Computer Science (9618 AS & A Level)

Paper 1 - Theory Fundamentals
Information Representation
Multimedia
Compression
Networks including the Internet
Computer Hardware
Processor Fundamentals
System Software
Ethics and Ownership
Databases
Paper 2 - Problem Solving & Programming Skills
Algorithms
Data Types & Structures
Programming
Software Development
System Software
Paper 4 - Practical Programming
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# Calculating Storage Sizes

Understanding how to calculate memory size required for different files requires us to learn the terms used for differnt memory sizes. We could calculate all memory sizes in bits (a single 1 or 0 in binary), but for most memory this would mean showing capacity in the many millions which is difficult.

Instead, we use a set of standard sizes that scale up as memory requirements get larger:

• 1 bit = a single 1 or 0
• 4 bits = a nibble
• 8 bits = a Byte

After a Byte, memory is calculated in one of two ways. If we are discussing the size of files or storage devices, multiples of 1000 are used. However, if we are discussing the transfer of data, multiples of 1024 are used.

Knowing this allows us to calculate how many files of a certain size can fit into another. For example:

David has a photo that is 2MB. How many of these can he store on his 3GB memory stick?

The first step is to put both in the same capacity:

`3 * 1000 = 3000`

Next, we can work out how many 2MB photos fit into 3000 MB:

`3000 / 2 = 1500`

So the answer is 1500 2MB photos could be stored on the disk if no other space is taken by other files.

## Activity

The Calculating Memory Size Scribbl.it Notes provide a structured way for you to revise topic areas in a visual way. You don’t have to be an artist as it’s all been drawn out for you (or you can use this as inspiration to create your own!). Print the notes, then colour in areas of importance, add doodles and colour, then add more detail to the notes page being as creative as possible.

## Activity – Exam Questions

Question 1

What is the defenition of a bit in Computer Science?



• A single binary digit. A bit will be either a 1 or a 0.

Question 2

How many bits are there in a nibble?



• A nibble has 4 bits. A nibble is equivalent to a single hexadecimal digit or half a byte.

Question 3

What is the maximum number that you can represent using a nibble?



• 1111 = 15 (or F in hexadecimal)

Question 4

What is the formula used to calculate how many unique numbers can be represented using a bit pattern?



• 2^n
• 2 represents the base, which in this case is binary
• n represents the number of bits in the bit pattern

Question 5

What is the difference between a kilobyte and a kibibyte?