Computer Science

What is a computer system?

Hardware and software working together to create a coded solution.

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State 4 reasons why humans are reliant on computer systems.

1) They allow people to contact and work with those all around the world. 2) They allow people to access their data securely from anywhere. 3) They improve the quality of life (those without limbs can get bionics)

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What is meant by 'reliability of computers'?

How dependable a computer is to do the job you entrust it with.

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State the three types of professional standards that must be considered when developing programs.

1) Ethical Considerations 2) Environmental issues 3) Law adherence

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State an example of an ethical consideration.

User privacy and public safety.

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State an example of an environmental issue.

Computers must be made as energy efficient as possible.

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State an example of why computer systems must adhere to the law.

A new computer system may plagiarise another's design. This violates patent rights.

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What is the Central processing unit?

The hardware that processes data in the computer.

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Processing data involves the Fetch-Decode-Execute Cycle. Explain this cycle.

The CPU searches and retrieves instructions from memory (FETCH). It then organises the instructions for specific parts of the CPU (DECODE). The CPU then executes the instructions (EXECUTE)

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The CPU interacts with other items in the computer. What does the CPU interact with.

The CPU interacts with items such as memory.

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What is clock speed?

The CPU needs a certain amount of cycles to execute an instruction. The faster these cycles can be completed, the more instructions can be executed per second.

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What is the effect of increased clock speed on CPU performance?

As clock speed increases, performance gets better.

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What are cores?

Cores are types of processors.

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What do cores do?

Cores allow multiple instructions to be completed at once.

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What is the effect of increased number of cores on CPU performance?

As number of cores increases, performance gets better.

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What is cache?

Cache is a type of memory that stores frequently accesed data so that they can be accessed faster at the next time of asking.

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What is the effect of increased cache size on CPU performance?

Performance gets better as cache size increases.

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What is binary?

Binary is a base two numbering system.This means that it consists of 2 digits; 0 and 1.

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Complete the sentence: In computer systems, everything is represented by binary. Binary can symbolise...

Voltage; either on (1) or off (0)

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What is a bit?

A bit is a binary which is either 1 or 0.

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How many bytes in a bit?

8

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Name the three main types of of logic gate.

AND, OR and NOT

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State the main details of the NOT gate.

This gate only has one input and output. It is an inverter, it reverses the inputs and outputs the the opposite.

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State the main details of the AND gate.

This gate has 2 inputs and 1 output. If A and B are both true, the output will also be true. If not, the output will be false.

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State the main details of the OR gate.

This gate has two inputs and one output. Either A or B have to be true for the output to be true. If both A and B are false, the output will be false.

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State the main details of RAM memory.

Have very quick read/write times. VOLATILE: loses everything stored on it when powered off. It's function is to store all of the data associated with the programs that are currently open. More Ram means that more programs can be open at any time.

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State the main details of ROM memory.

Contains pre-recorded data, so the data can't be altered, it can only be read. NON-VOLATILE: data is retained when the system is powered off. Used mostly in PCs to store essential programs. Used in simple devices for calculations.

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When does virtual memory come into effect?

When the RAM is used up.

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What happens to data in the RAM that hasn't been accessed recently?

It is sent to be stored temporarily on a section of the hard drive that extends the RAM capacity.

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Comment on the time taken to access virtual memory.

Virtual memory is accessed very slowly because of the slow read/write times.

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What is cache memory?

It's a store of data that allows future requests to be served quicker.

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Comment on the read/write times of cache. What happens to frequently accessed data?

Cache memory has very fast read/write times. Frequently accessed data is stored into cache memory.

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Describe Flash Memory.

Non-volatile. It has no mechanical parts. This makes it more reliable. Flash memory uses solid state technology.

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Name some common input devices.

Mouse, Keyboard, Webcam etc.

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Name some common output devices.

Printers, Speakers, etc.

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Name two devices that can be classified as input and output devices.

Screens/monitors and microphones.

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Recall the two types of input/output devices fon users with specific needs.

Eye-tracking control and Braille devices.

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Who is eye-tracking control designed for? How does eye-tracking control work?

Designed for people who cannot use a keyboard and mouse. The user can navigate through the interface just by moving their eyes.

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Who is braille designed for? How does braille work?

Designed for blind or visually impaired users. Braille keyboards can be used to input text. Braille output devices such as braille displays, printers and voice synthesizers are available.

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State two reasons why RAM can't be used to permanently save out files.

1) RAM has a small capacity. 2) RAM loses everything stored on it once the computer system is powered off- it is volatile.

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Why is secondary storage needed?

Secondary storage is needed because it retains data after the system is powered off - it is non-volatile.

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Name the three main types of secondary data.

Optical, magnetic and solid state.

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How does optical storage work?

Data is written when a laser 'burns' dents into the medium. Light that hits a dent will reflect differently to light that hits a flat spot, allowing the optical drive to detect differences and therefore read the binary data.

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State two advantages of optical storage.

Fairly reliable and durable. Good portability.

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State two disadvantages of optical storage.

Easily damaged (through scratches) and has a small capacity (usual

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State two disadvantages of optical storage.

Easily damaged (through scratches) and has a small capacity (usually less than 1GB

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How does solid-state work?

Consists of complex logic gates (It is non-mechanical).

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State the advantages of solid-state storage.

Fast storage, Very reliable (as they're non-mechanical), Fairly portable.

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State the main disadvantage of solid-state storage.

It can be quite expensive to buy.

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How does magnetic storage work?

Read and write using electromagnets. Storage surface is either magnetized (1) or not magnetized (0)

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State some advantages and disadvantages of magnetic storage.

Advantages include it's large capacity, cheap price and it's reliability. Disadvantages include it's poor durability and portability.

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What is a character?

A unit of information - usually a letter, number or symbol.

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How do character sets allow the user to input or output characters?

A charactr set translates a character into binary code - and back again.

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What is ASCII?

ASCII is a character set that is based on the English Language.

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How many specific characters can ASCII represent?

ASCII can represent 256 characters as 8 bit binary numbers.

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Can extra characters be added to ASCII?

No extra characters can be added so languages with non-English letters (such as Gujarati) cannot use ASCII.

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Recall some details about Unicode.

Uses the first 256 characters from ASCII. It is based on 16 bits and can represent at least 65,536 characters meaning that other world language characters can also be used.

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What is the operating system?

The software that links hardware and other software together.

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State the three functions of the operating system.

User interface, Request Authentication and Peripheral device compatibility.

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What is the user interface?

The layout and functions of the software that the user sees. Command line interfaces have been replaced by Graphical User Interfaces (GUIs)

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What is request authentication?

The operating system verifies each request to distinguish between legitimate and illegitimate program requests (for security).

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What is a peripheral device?

A piece of hardware that interacts with the computer e.g. a keyboard or monitor

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Utility programs can be classified into three categories. State these.

Security, Disk Organisation and System Maintenance.

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State and explain the security measures taken by the computer.

ANTIVIRUS- A program that detects and eliminates malicious software. FIREWALLS- a network system that controls and filters incoming and outgoing traffic. SPYWARE PROTECTION- these programs block the spyware threat and try to eliminate it.

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State the three measures taken to organize disks in a computer.

Formatting, file transfer and defragmentation.

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What is Formatting? What is File Transfer?

FORMATTING- the process of partitioning sections of secondary storage before file storage. FILE TRANSFER- allows files to be moved around, copied and deleted by the user.

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What is defragmentation?

Related data can be scattered on different parts of the hard disk. Defragging a disk reorganizes related data, so it is accessed quicker.

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State the two measures of 'system maintenance'.

System clean-up tools and system diagnostics.

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What is the role of system clean-up tools? What is the role of System Diagnostics?

SYSTEM CLEAN-UP TOOLS- this improves the system performance as old files are deleted. SYSTEM DIAGNOSTICS- the specifications of the hardware are kept and can be checked to see if they are functioning correctly.

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What is custom written software? State the advantages and disadvantages.

Custom written software is software that meets the needs of the customer perfectly. This is also the main advantage. The disadvantages include long production times, high price and no assistance available if something goes wrong.

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What is 'off the shelf' software?

'Off the shelf' software is software that is aimed at meeting the needs of many people (e.g. Microsoft Word).

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State the advantages and disadvantages of 'off the shelf' software.

The main disadvantage is that it may not be relevant to the needs of a specific customer. Advantages include its cheap price, the abundance of help available and the fact that 'off the shelf' software is usually bug free.

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What is open source software? What are the advantages?

Software whose source code is freely available. Open source software is most often free and can be modified.

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What is proprietary software? What are the advantages?

Commercially available software sold in the form of a license. Disadvantages may be that the software may not be specific to the users needs and also that the software can't be reverse engineered. Free updates and complete testing are available.

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What are images?

Images are a series of pixels represented in binary.

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Recall the main details to do with images.

Most images are examples of analogue data. A computer must digitalise any image to interpreted its features (e.g. colours)

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Describe how pixels are used to make images.

The computer finds an average colour for each pixel and assigns it a binary value. Black and white are either one or zero. Every colour is just a mix of red, blue and green. So, each pixel is represented as a shade of blue, red or green

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What is a pixel?

Pixels are minute areas of illumination on a display screen

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What is colour depth?

Number of bits that can be used to represent the colour of a pixel.

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State the relationship between colour depth and file size.

As colour depth increases, file size increases.

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Which will have more colour combinations; images represented by bytes of nibbles?

Images represented by bytes.

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What is resolution?

The detail that an image holds, measured in dpi (dots per inch)

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State the relationship between file size and resolution.

As resolution increases, file size also increases.

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What is metadata?

The data about a file that is automatically stored with it.

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Give an example of metadata.

If a picture is taken by a camera, the camera may save additional information about the image, even though the information may not be very important. An example of metadata would be the height and width of an image.

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What type of wave are sound waves?

Mechanical wave- they work through movement.

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What type of data is sound?

Analogue.

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Sound is defined by two elements. State these two elements.

Frequency (number of wave cycles per second, Hertz, Hz) and Amplitude (height of the wave)

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State the relationship between amplitude and volume (decibel level).

The greater the amplitude, the greater the volume (decibel level)

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What is sampling another way of saying?

'Digitalising' sound.

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What is the rate of sampling?

Rate of sampling is how often the computer takes a reading of the sound waves per second.

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State the effect of greater rate of sampling on sound quality and file size.

A greater rate of sampling results in greater sound quality, but larger file size as more data is stored.

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What is bit depth and how does bit depth affect sound quality?

Bit depth is the amount of bits that represent the sound file. For example, sound represented by a nibble will have worse sound quality than audio represented by a byte.

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Place the following into low or high level programming languages: Assembly Languages, C++, Language, Python and Javascript.

Low level: Assembly Languages -----> High level: C++, Javascript, Python, Language.

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What is machine code? Can machine code be understood by non-programmers?

Machine code is the raw instructions used by the CPU - in the form of bit patterns. Non-programmers cannot understand machine code.

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What are bit patterns? What is machine code written into?

Bit patterns convert high-level instructions into machine code. Machine code is written in the form of patterns of bits (binary digits, 1 and 0)

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High level instructions can be split up into two components. State these two components.

The opcode and the operand.

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What is an opcode?

Part of the instruction which specifies the operation to be carried out. For example, the add sign in the sum "00001000+00100010" is the opcode.

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What is an operand?

Part of the instruction which supplies the data. For example, the binary bits in the sum "00001000+00100010" are the operands.

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Describe instruction sets.

The opcode is given by an instruction set which is unique to the processor. Each operator has a unique binary representation, but it can of course be repeated in a bit pattern.

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The opcode and the operand may be represented by the same bits. The processor must distinguish between these two. Explain how the processor does this.

It does this by simply knowing the position of the opcode and operand (in the sequence).

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What is a database?

A database is simply a persistent, organised store of data.

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Databases can exist in non-digital and digital forms. Give an example of a non-digital database.

Non-digital forms can exist in the form of written directories and registers.

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What must be used to create digital databases?

Specialist data handling programs.

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State some details about specialist data handling programs.

They are a type of proprietary software that are available to buy, but are often very expensive.

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What does DBMS stand for?

Database Management System

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What is a DBMS? Give an example of one.

A DBMS is a program that handles databases. An example of a DBMS is Microsoft Access; it allows you to create, maintain and interrogate (extract information from it) a database.

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Complete the sentence: "DBMSs are......"

secure and allow multi-user access because it allows a sense of separation from other applications.

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What are the three features of a DBMS?

1) It provides a set of tools for accessing and maintaining the database. 2) The DBMS will automatically check for issues (validating the stored data). 3) Controls access to data.

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Give examples of how a DBMS provides a set of tools for accessing and maintaining the database.

It can create tables and run queries etc.

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Explain how "The DBMS will automatically check for issues (validating the stored data)"

When the DBMS is set up, it can be customised for specific purposes. For example, it can be customised to validate specific things like currency and web domain etc.

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Why is it good that the DBMS controls access to data?

This is good for security reasons and multi-user database access at any one time.

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What is a relational database?

A relationship consists of tables linked together with each other by key fields.

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Recall the six components of relational databases.

Entities, tables, forms, queries, reports and modules.

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What are entities?

The things that data has been collected about

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What are tables?

2D representations of data that is stored in rows and columns.

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What are forms?

What data is submitted to databases in.

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What are queries?

These are requests for data from the database.

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What are requests?

Presentations of data from the database.

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What are modules?

Things that add additional functionality to the database.

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Tables contain data from entities. What do the table's columns and rows represent?

The columns are usually the table entities. The rows contain the data associated with the entities.

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What are logical operators?

Different words or symbols (called operators) are used to retrieved data that is wanted.

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State the three logical operators and give examples of each.

1) Boolean (AND, OR, NOT) 2) Arithmetic (+add and -subtract and /divide) 3) Comparison operators (==,

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What is data redundancy?

Data redundancy is when data is unnecessarily repeated in two or more tables. This is inefficient and shouldn't occur in a well designed databases.

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What are key fields?

Key fields are unique identifiers in each table that links that specific table to at least one other.

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What is input validation?

Validation is the act of checking something to make sure it is correct and reasonable.

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State the four methods of input validation.

1) Data type 2) Range Check 3) Null Check 4) Length Check

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What does the 'data type' validation do?

Ensures that the input is a specific data type (e.g. age must be an integer)

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What does the 'range check' validation do?

Checks that the input is in an appropriate range (data must be between 1 and 31).

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What does the 'null check' validation do?

Makes sure a database field isn't left blank.

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Computer Science

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