AQA GCSE Computer Science Paper 2: Computing concepts November 2020 question paper 8525/2

State the decimal representation of the binary number 10010100

State the hexadecimal representation of the binary number 10010100

State the hexadecimal representation of the decimal number 143

You should show your working.

State the binary representation of the hexadecimal number BE

You should show your working.

Give two reasons why hexadecimal is often used instead of binary in computer science.

State the result, in binary, of performing a binary shift two places to the left on the binary value 00111001

What is the largest decimal number that can be represented using 6 bits?

How many bits are there in 5 kB?

You should show your working.

Explain how a sound wave is converted so that it can be stored in a computer.

A student has recorded a 30 second digital sound track using a sample rate of 44 000Hz. 8 bits have been used to store each sample taken.

Calculate the file size in kilobytes of the digital sound track.

You should show your working.

Shade one lozenge to show which statement best describes data compression.

Give two reasons why data compression is often used.

Run length encoding (RLE) is one method of compressing data.

State the feature of data that allows it to be compressed effectively using RLE.

Describe how RLE works. In your answer you must use an example.

Shade three lozenges to show which of the following are essential components of the Von Neumann architecture.

Main memory is any form of memory that is directly accessible by the CPU, except for cache and registers.

Explain how main memory is used.

The cost and physical size of RAM and secondary storage are normally different.

Describe two other differences between RAM and secondary storage.

An operating system manages the memory of a computer.

State two other things that are managed by the operating system.

Figure 1 shows a Huffman tree that has been created to represent the string shown in Figure 2.

Figure 2

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A student was asked to describe how a Huffman tree could be created for the string in Figure 2. Her response was:

“I would count the number of times each character appears in the string and create a frequency table sorted alphabetically. For example, the letter S has the highest frequency in Figure 2. Next I would take the two characters with the largest frequencies and combine them into a new node. The new node would be added to the end of the frequency table. The two characters with the lowest remaining frequencies are now combined into a new node and the process is repeated until all the characters have been added to nodes and the tree created.”

State four mistakes the student has made in her response.

When the Huffman tree in Figure 1 is used, the string in Figure 2 can be represented using 130 bits.

The 36-character string shown in Figure 2 could also be encoded using ASCII.

How many bits are saved when Huffman coding is used rather than ASCII to represent the string shown in Figure 2 ?

You must show your working.

Define the term ‘computer network’.

Computer networks can be wired or wireless.

Discuss the advantages and disadvantages of wired and wireless networks.

In your answer you should:

• discuss the advantages and disadvantages of each network type

• compare the security of wired and wireless networks.

State which layer of the TCP/IP model each of the network protocols operates at by ticking one box in each row of Table 1.

Define the term ‘cyber security’.

Define the term ‘malware’.

Explain how each of the following cyber security threats could be used by a student to gain unauthorised access to a school network:

• weak and default passwords

• misconfigured access rights

• removable media

• unpatched and/or outdated software.

In your answer you should also describe some possible consequences of these threats.

Shade one lozenge to show which statement best describes the definition of the term ‘social engineering’.

Phishing is a form of social engineering.

Describe two methods a school could use to protect its staff and students from phishing.

A healthcare publication contains the following article.

This item cannot be reproduced here due to third-party copyright restrictions.

Explain two potential legal and/or ethical impacts of using implanted microchips in healthcare.