Edexcel GCSE Computer science key questions

Advantages of Artificial intelligence

1. AI can perform tasks instead of humans. 2. AI can have the ability to learn. 3. Very good at parallel processing. 4. AI can solve complicated problems accurately.

Components of a hard disk drive

1. Actuator axis 2. Actuator arm 3. Head 4. Spindle 5. Platter

Benefits of using subprograms when writing software solutions

1. Are written only once. 2. Therefore, can be called from anywhere in the program. 3. Needs to be debugged only once. 4. Makes the main program shorter. > More readable. 5. Reduces the need for global variables. 6. Can be used to hide complex coding. 7. Can be reused in other programs.

Disadvantages of nanotechnology

1. Atomic weapons could become more accessible and dangerous. 2. Expensive. 3. Difficult to manufacture. 4. Respiratory problems can arise from breathing in nanotech products.

Disadvantages of decomposition

1. Badly understood problems are hard to decompose. 2. Solutions to sub-problems might not combine to solve the original problem.

Hardware components of a computer

1. CPU 2. Memory 3. Storage devices 4. Input devices 5. Output devices 6. Communication devices

Rules for naming variables

1. Can start with letter or underscore. 2. After first character, it can include letters, numbers and underscores. 3. Can be one letter long but not one number long. 4. Cannot be a word that the programming language has reserved for use (e.g. 'boolean').

Advantages of a mesh network

1. Can withstand high traffic as data can be transmitted from different devices simultaneously. 2. If one of the device in the network crashes, there are other routes available for the data to be transmitted. 3. Expansion and modification can be done without interrupting other devices.

Factors influencing performance of software

1. Choice of appropriate data structures. 2. Choice of appropriate algorithms.

Quantum computing

1. Computers use qubit (quantum bits). 2. Qubits can be 0, 1 or both at the same time. 3. Increased speed of processing in computers/ increase numbers of instructions done per second. 4. Current materials need super-cooling. 5. Very expensive because of hardware needed. 6. May be used to solve problems not considered solvable by conventional computing. 7. May lead to current algorithms being easily broken. 8. Can be used to perform millions of calculations in parallel. Eg: used in security, vision recognition, medical diagnosis

Components of a CPU

1. Control unit 2. Arithmetic logic unit (ALU) 3. Registers 4. Internal clock 5. Internal buses 6. Logic gates

Decode

1. Control unit decodes instruction into control signals. 2. Control unit determines what kind of instruction it is.

Fetch

1. Control unit goes to address in memory specified by program counter to retrieve instruction. 2. Control unit makes a copy of the instruction and places it in the instructions register. 3. Program counter is updated to hold the address of the next instructions.

Execute

1. Control unit sends signals to the ALU to carry out the processing. 2. The output is stored in a different register or in RAM.

Main tasks of the operating system

1. Controls and organises hardware and software. 2. Manages security. 3. Provides user interface.

Mean algorithm

1. Count how many indexes there are in the list. 2. Add up all the numbers in the list. 3. Divide the sum of the numbers by the length of the list +1 (because of zero-indexing).

Disadvantages of magnetic hard disk

1. Crashes damage surface of disk, leading to loss of data. 2. Easily damaged if dropped. 3. Have moving parts which eventually fail. 4. Use large amount of power compared to other storage media. 5. Can be noisy.

Maximum / minimum algorithm

1. Create two variables - one for the minimum value and one for the maximum value. 2. Compare the first pair of elements. Make the smaller one the minimum variable and the larger one the maximum variable. 3. Repeat step 2 with every pair of elements after the first pair. The first variable will be the smallest element and the second variable will be the largest element.

Magnetic storage

1. Data is stored in a digital format on the magnetic surfaces of the disks. 2. Data is stored on the surface in sectors and tracks. 3. A sector on a given track will give a fixed number of bytes.

Advantages of decomposition

1. Different people can work on different sub-problems at the same time. 2. Maintenance is easier. 3. Parallelisation is possible.

Disadvantages of optical storage devices

1. Easily broken. 2. Easily scratched or damaged by heat and light. 3. Expensive per GB compared to other storage media. 4. Require special drives to read and write. 5. Data on write-once disks is permanent. 6. There are no standards for longevity tests.

Advantages of a bus network

1. Easy cable management, so easy to install. 2. Cheap to install. 3. Each device is isolated - if it breaks, the rest still works. 4. Very suitable for small networks.

Advantages of optical storage devices

1. Easy to use. 2. Easy to store and carry. 3. Long-lasting if looked after properly. 4. Read in many devices such as audio and television systems.

Twisted pair communication medium description

1. Electric signal communication through inner conductors of wires. 2. Medium noise contamination. 3. Slightly affected by external magnetic interference. 4. Medium bandwith. 5. Reasonably easy to install. 6. Medium cost compared to coaxial and fibre optic.

Coaxial communication medium description

1. Electric signal communication through wires. 2. High noise contamination. 3. Quite affected by external magnetic interference. 4. Low bandwidth. 5. Easy to install. 6. Lowest cost compared to twisted pair and fibre optic.

Encryption

1. Encryption such as provided by the VPN 2. Ensures that private or sensitive data which is sent over the Internet 3. Cannot be understood by unauthorised users ( such as hackers ). > Data is unintelligible to third parties. 4. Reduces the risk of companies losing important data > E.g. private customer details or company secrets > Could have financial or legal impacts.

Advantages of DNA computing

1. Extremely fast compared to conventional computing. 2. Very light in terms of weight. 3. Requires less power than conventional computing. 4. DNA computers have a much larger storage capacity than conventional computers. 5. It is evolvable and can respond to external stimuli.

Disadvantages of ring network

1. Failure of any cable or device can cause the entire network to crash. 2. Maintainance or alterations being made to one of the devices can affect the performance of the whole network.

Advantages of nanotechnology

1. Faster components can be made. 2. Smaller components can be made. 3. It is more energy efficient.

Advantages of quantum computing

1. Faster than conventional computing. 2. More powerful than conventional computing. 3. Requires smaller devices than conventional computing. 4. Could solve problems that are currently impossible to solve in the normal timespan.

Functions of the operating system

1. File management - Know the address in memory where each file is - Know which users have access to which files, - Present files in a structured form. 2. Input/output - Control how I/O devices are used by programs. 3. Resource allocation - Give the right resources to programs for execution - Ensure that enough memory is allocated to each program. 4. Process management - Allocate resources to programs only when they are needed - Switch between processes and give higher priorities to more important processes. 5. Network management - Manage users connected to computer - Facilitate shared access to resources - Have high standards of security. 6. User management - Create different profiles - Store usernames and passwords.

Disadvantages of quantum computing

1. Hard to control quantum particles. (photons) 2. More expensive than conventional computing. 3. Difficult to build. 4. Produces a lot of heat.

Characteristics of subprograms

1. Has a single entry point. 2. There is only one subprogram execution at a time.

Disadvantages of a mesh network

1. High chance of redundancy in many of the networks. 2. High cost. 3. Difficult maintainance.

Factors affecting algorithm efficiency

1. How well designed the data structures are. 2. Software and hardware that the algorithm runs on. 3. Programming language and translator used.

Disadvantages of computer networks

1. If a file server breaks down, the files contained in it becomes inaccessible. 2. Cost of cabling and file servers can be high. 3. Management of large networks is complicated. > A specialist needs to be employed. 4. If a virus gets in the system, it can spread easily. 5. Risk of hacking - security measures are required > E.g. firewall

Disadvantages of a bus network

1. If the backbone breaks, the network crashes. 2. Backbone length restricts the number of devices that can be connected to it. 3. The more computers you add to it, the slower the performance of the network because of data collisions.

Disadvantages of a star network

1. If the hub node crashes, the whole network fails.

Advantages of using hexadecimal notation

1. Less storage space is used. 2. Easy to convert back and forth from binary. 3. 1 hex digit represents 4 bits. 4. Easy for humans to read. 5. Hex is used to represent colours in webpages. 6. Hex is often used in error messages on your computer. > Hex number refers to the memory location of the error. > Helps programmers to find and fix problems.

Disadvantages of solid-state disks

1. Limited storage capacity compared to magnetic drives. 2. Cost per GB is more expensive than magnetic drives. 3. Write speeds can be four times slower than magnetic drives. 4. Data can be erased and written about 100,000 times.

Lossless compression

1. Looks for patterns of repeated data and represents them in a shorter form. 2. Original data can be retrieved with no loss of quality.

Types of secondary storage

1. Magnetic 2. Optical 3. Solid-state

Nanotechnology

1. Manipulation of matter on a very small account. > About 1 to 100 nanometers 2. Most biological processes occur at this nanoscale. > Quantum phenomena starts to occur. 3. Electronic devices use nanomaterials. > Structures at this nanoscale. > Nanoscale transistors are faster, more powerful and more energy efficient. 4. The limit for pure silicon is 10 nm. > IBM recently made working chips with transistors 7nm long. > 7nm chips will be commercially ready in 2017. 5. Memory technology is being developed with nanotechnology. > E.g. nanodots > Tiny magnets which can have their polarity switched to represent the binary digits. > Increases memory density. > Store more data in a smaller amount of space. 6. Nanoparticles could be much more toxic. > Can pass through membranes which larger molecules can't 7. May also allow people to create more powerful weapons.

Advantages of a ring network

1. Message passes through all intermediate device, so no central server is needed.

Disadvantages of DNA computing

1. Much more expensive that conventional computing. 2. Difficult to build. 3. Errors are common due to complexity of DNA. 4. Simple problems take longer to process than in conventional computing.

Solid state storage

1. No moving parts, and therefore is more reliable compared to HDD. 2. Lower power consumption. 3. No heat generated. Consumes less energy. 4. Short-lived.

Advantages of magnetic hard disk

1. Non-volatile. 2. Cheap per GB compared to other storage media. 3. Easily replaced and upgraded. 4. Very large storage capacity. 5. Store and retrieve data faster than optical disks.

Parameters of bitmap

1. Number of pixels. 2. Colour depth of pixels.

Advantages of a star network

1. Offers operational simplicity. 2. Each device is isolated > If one device or cable breaks, the rest still works.

Types of system software

1. Operating system 2. Utility programs

Fibre optic communication medium description

1. Optic signal through glass fibres. 2. Very low noise contamination. 3. Not affected by external magnetic interference. 4. High bandwith. 5. Hard to install. 6. High cost compared to coaxial and twisted pair.

Types of non-functional testing

1. Performance test (speed) 2. Robustness test (response to bugs) 3. Security test (unauthorised access, attacks...) 4. Load test (behaviour during increasing system loads) 5. Stress test (behaviour when overloaded) 6. Volume test (behaviour relative to quantity of data)

Secondary storage

1. Permanent storage 2. External devices like CD, floppy magnetic discs etc. 3. Secondary storage cannot be directly accessed by the CPU and is also external memory storage.

Server-side

1. Permanent storage can be accessed. > E.g. using SQL to query database 2. User input can be processed. 3. Server side programming language includes C++, Java, C# (most languages can be used).

Why should constants be used in programs?

1. Readability > Makes it understandable for the readers. > Not everyone will know the relevance and understand what the literal values mean. 2. Ability to update > If the value of the constant needs updating, it only has to be done once instead changing all of the occurrence of the value. 3. Compiler optimisation > Depending on the compiler, use of named constants can lead to optimisation. > Either by improving performance or by reducing memory space.

Reasons for compressing data

1. Reduce download time. 2. Reduce storage used.

Advantages of client-side processing

1. Reduces the workload of the server which can potentially speed it up. 2. Allows for more instant responses. > If inputs can be validated by the client, then it saves a trip to the server. > Reduces overall web traffic. > Less chance of errors.

Lossy compression

1. Removes some data from the original data. > E.g. if two pixels are almost the same colour, it might make them the same colour. 2. The removed data cannot be retrieved. 3. Data which is compressed using lossy compression tends to loose its quality especially images.

Components of a computer network

1. Servers 2. Clients 3. Communication media 4. Network adapter 5. Resources 6. Protocols 7. Users

Advantages of server-side processing

1. Servers are usually powerful > Processing is faster 2. No software plugins are needed to be installed on the user's computer. 3. Any patches or updates only needs to be applied to the server.

Reasons for encrypting data

1. So that data is not intercepted by unauthorised / third party users. 2. To verify the sender of the data.

Components of any electronic communications process

1. Source of information. 2. Transmitters > Converts the information from the source into digital signals. 3. Communications media > Moves the signal. 4. Receiver > Converts the digital signals into a form the destination can understand. 5. Destination of information.

Artificial intelligence (AI)

1. Study of creating machines and software exhibiting signs of intelligence. 2. Aim is to build autonomous machines. > Machines that can carry out complex tasks without our constant involvement. > These are intelligent agents. > Take in and respond to external changes. 3. Some modern robots (an autonomous agent) have the ability to learn in a limited capacity. > E.g. Mimicking the actions of humans. 4. Some AI is built to try and replicate some properties of our brain. > E.g. Google DeepMind using neural networks. > Think of neural networks as in neurons in the brain. 5. Causes them to work differently to normal computers. 6. Basically the neural networks are rewired to be more efficient compared to humans in mathematical calculations. > Makes it faster. 7. AI systems have the ability to learn. > Can be much more accurate. > Can detect and solve problems on their own. 8. Can do boring, repetitive tasks that humans don't like. > Standard of living increases. > Causes unemployment > Ethical dilemma 9. Fear that AI could eventually replace humans, should they become superintelligent. > Exceed human capabilities in everything.

Primary storage

1. Temporary storage 2. Main memory (Hard disk, RAM) where the operating system resides.

Resolution

1. The amount of detail an image holds. 2. Measured in dots per inch (dpi) or also pixels per inch (PPI). 3. Also defined as the number of pixels contained in a display monitor.

Process for communication in the client-server network model.

1. The client uses the address of the server to make a connection. 2. The client sends a request to the server. 3. The server obtains the address from the client once the client makes a connection to the server. 4. The server sends the requested data to the client.

Client-Side

1. The interactive web pages are made and things can happen dynamically. 2. Temporary storage can be interacted with. > e.g. cookies 3. Programming under the client-side can be done using Java script and HTML and CSS are used.

Relationship between the Internet and the World Wide Web (WWW)

1. The internet is made up of millions of small computer network. 2. A large part of the Internet is the WWW. 3. The WWW is made up of web pages that have one or more web pages. 4. The Internet is a hardware and the WWW is the information stored in the hardware.

Components stored in a RAM

1. The operating system 2. Applications 3. The graphical user interface (GUI)

Ways which subprograms can gain access to data that is being processed.

1. Through variables. 2. Thorugh parameter passing. (more flexible)

Measures of algorithm efficiency

1. Time measure (number of memory accesses performed, number of comparisons etc.). 2. Space measure (amount of memory the algorithm takes, amount of input to the algorithm).

Advantages of two's complement over sign and magnitude.

1. Two's complement has only one value for 0. 2. Sign and magnitude has two values for 0. 3. Addition of binary numbers will always work in two's complement. 4. Addition of binary numbers might not always work in sign and magnitude.

Advantages of computer networks

1. Users can share files easily. 2. Users can share software stored in the main system. 3. Clients can share common peripheral devices, saving money. 4. Network software licences are less expensive than several standalone licences. 5. Users can communicate (email, messenger, etc). 6. Backing up data is much more straightforward. 7. Security is of a high standard.

DNA computing

1. Uses DNA, biochemistry and molecular biology as the material to make the processors rather than those currently based on silicon. > The processors made from silicon will eventually reach their limits of speed and how small we can make them. 2. DNA molecules are what carry our genes. > Store biological information about us. 3. Genes code for a specific protein. 4. Genes are represented by the four bases : Adenine, Cytosine, Guanine and Thymine. > Contrasts with the two bits of information stored in the binary system. 5. Despite having a large supply of silicon, it needs to be highly purified for electronics. > Expensive 6. DNA has a large supply > Comparatively cheaper 7. Can be many times smaller compared to the current computers. > Much better at parallel processing. 8. DNA might not survive long enough to get a result. > Has a half-life of 520 years 9. Other biological building blocks (e.g. enzymes) have also been able to be used to execute instructions. > Sometimes in combination with DNA. 10. This biological technology is evolvable, self-replicating, self-repairing and is responsive to external stimuli.

Reasons for using virtual machines

1. Using applications that are not available on the host operating system. 2. Testing an application or file to see if it's dangerous without the possibility of damaging the host operation. 3. Creating a machine with the same operating system as the host machine and checking the effect of changing or deleting files without damaging the host machine.

Advantages of solid-state disks

1. Very durable. 2. Free from mechanical problems. 3. Lightweight. 4. Read speeds are faster than hard-disk drives. 5. Require less power than magnetic drives. 6. Silent.

Finding the IP address from the domain name

1. Web browser (client) connects to a DNS server to check whether the domain name is in its database. 2. DNS server checks. > If it isn't there, it acts as a client and searches other DNS servers until it finds it. 3. When the IP address is found, it is sent to the web browser, so it can access the page.

Client / Server Side

1. When the web page is loaded, a request is made to the domain name server (DNS). 2. This translates the URL into an IP address. 3. This is used to contact the web server. 4. The host then serves the web page to the browser which is interpreted and then displayed on the user's computer. 5. Some processing can be done by the client-side. > e.g. browser 6. Some processing can be done by the server-side. > e.g. web server

Disadvantages of Artificial Intelligence

1. Will cause unemployment. 2. Could bring about superintelligent robots that can be a threat to humankind.

Types of communications media

1. Wireless 2. Coaxial (cable) 3. Twisted pair (cable) 4. Fibre optic

Uses of databases

> To gather, organise and analyse data efficiently. 1. Add new data, edit data or delete old data. 2. Data can be sorted easily, therefore, it is easier to search for a particular record. 3. Multi-access. 4. Stores very large numbers of records efficiently. 5. Data can be imported into other applications. > E.g. mail-merge letters to customers.

Operating system

Collection of software that links hardware and other software together. Manages computer resources. Creates the user interface and running applications.

Fetch-decode-execute cycle

FETCH :Copy PC onto address bus and read from RAM :RAM content comes back on data bus to IR :Increase PC by 1 DECODE :CU examines instructions and fetches required data :CU puts the address of the required data on the address bus - RAM :RAM puts contents of that address on that data bus :Put data in R0 EXECUTE :Copy R0 into ACC

Steps to improve security of important data

Using encryption ___________________ 1. Encryption such as provided by the VPN 2. Ensures that private or sensitive data which is sent over the Internet 3. Cannot be understood by unauthorised users ( such as hackers ). > Data is unintelligible to third parties. 4. Reduces the risk of companies losing important data > E.g. private customer details or company secrets > Could have financial or legal impacts. Creating passwords _____________________ 1. Logon passwords. 2. Passwords should be required to log into the computer and access data. 3. Passwords should be strong. > mixed case, letters, numbers and symbols 4. Passwords should be changed regularly. 5. Passwords reduce the security risk if the computer is stolen or lost. 6. Because unauthorised users will not have access to the data stored on it.

Issues surrounding computing

mnemonic (kind of) : SEEL 1. Social > Cyber bullying > Trolling > AI (Artificial intelligence) causes unemployment > Freedom of speech 2. Ethical > Copyright laws > Is victimless crime a crime > There might not be such a thing as victimless crime 3. Environmental > Resource depletion > Computer resources uses quite a lot of non- renewable resource > E.g. copper in wires, gold > Don't use much gold, however, the gold use is thrown in a landfill > Waste of gold. > Apple gains revenue by taking scraps of gold from thrown away iPhones. 4. Legal > Fraud > Criminal activities online