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Computer science revision guide, The fetch-decode-execute cycle (FDE),…
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Threats
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Malware- any kind of malicious program that is installed on a computer with the intent to cause damage
Viruses- a computer program hidden in another computer, the virus code is only run when the host program is executed. They can delete data or change system files so data becomes corrupted
Worms- Do not need to be hosted in another program. They often create a back door so that a hacker can take over an infected computer. Worms are self replicating
Trojans- programs the user are tricked into installing under the pretence that they are legitimate and useful
Ransomware- malware that interferes with a users operation of a computer unless a sum of money (ransom) is paid
Spyware- malware that comes packaged with other software such as free software the user downloads. It gathers information about a user and sends it to the criminal
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Social engineering
Phishing- uses fake emails and websites to trick people into giving away their sensitive data and information
Pretexting- the criminal invents a scenario where to persuade the victim to divulge information they may not do otherwise
shouldering- involves finding out login details, passwords and pins by watching people enter them
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Brute force attacks- When a hacker attempts to crack a password by systematically trying different combinations of letter and numbers until the correct one is found
Denial of service (DoS) attacks- Attacks designed to bring down servers or websites by flooding them with superfluous bogus requests such as repeated attempts to log in. This uses up internet bandwidth and prevents the servers from responding to legitimate requests
The concept of SQL injection- Many websites use databases to store the details of users. Structured Query Language(SQL) is used to search these databases , for example to check a users login credentials are correct
SQL injection can be used to bypass security and circumvent the need to enter legitimate login credentials, thus allowing hackers to gain access to the database
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CPU definitions
Arithmetic logic unit (ALU) - operations such as add, subtract, multiply, divide / logical operations such as AND,OR and NOT and the result of "less than" "greater than" "equal to" comparisons / binary shift operations (multiplication and division) / the ALU carries out the calculations and logical decisions required by the program instructions that the CPU is processing
Control unit (CU) - coordinates the activity of the CPU by fetching and decoding instructions from memory and sending out signals to control how data moves around the parts of the CPU and memory, in order to execute these instructions
RAM-Random access memory (RAM) is the hardware in a computing device that provides temporary storage for the operating system (OS), software programs and any other data in current use so they're quickly available to the device's processor.
registers - memory locations within the CPU that hold data temporarily and can be accessed very quickly. Their role in the CPU is to accept, store and transfer data and instructions for immediate use by the CPU. Used during the FDE cycle
ROM-Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device.
Cache memory is to provide temporary storage that the CPU can access very quickly
Its role in the CPU is to store instructions and data that are used repeatedly or are likely to be required for the next CPU operation
A user should consider :
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Durability - how robust is the medium, and how robust will it need to be?
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Networks
Star topology
has a central switch which all other devices connect to, A switch is an intelligent device which ensures that traffic only goes to the intended device
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Mesh topology
a type of computer network in which each node (computer or other device) is connected to every other node in the network
Wide area networks (WAN) - a network of computers that spans a large geographic area, often between cities or even across continents
Local area networks (LAN) - A network of computers in a small geographic area, such as a single building
Memory
Both RAM and flash memory are a form of storage. However, RAM is temporary, while flash memory is permanent. Flash memory stores data even after the power is turned off, but it also has a limited lifespan. After a set amount of write actions, flash memory loses its ability to store data.
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Flash memory, also known as flash storage, is a type of nonvolatile memory that erases data in units called blocks and rewrites data at the byte level. Flash memory is widely used for storage and data transfer in consumer devices, enterprise systems and industrial applications.
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processor cores - Each core can fetch and execute instructions independently so a multiple core processor can handle several instructions at the same time. While they these multiple cores can work on separate programs or parts of a program at the same time, this is only possible if the program has been written to take advantage of multiple cores. The task that the program is attempting must also be one that can split up into subsections to take advantage of multiple cores
A dual-core processor has two cores allowing it to handle multiple tasks simultaneously, while a single-core processor has only one core, limiting it to one task at a time
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Von Neuman architecture
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memory address register (MAR) - stores the address of the location in memory for data to be fetched from or sent to
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Legislation
COMPUTER MISUSE ACT 1990
it is a criminal offence to make any unauthorised access to computer material with intent to commit further offences (for example blackmail) or with the intent to modify the computer material (for example distributing viruses
the first provision refers to unauthorised access (commonly called hacking)
the second provision refers to anything that impairs the performance of a computer system including the distribution of viruses
DATA PROTECTION ACT 2018
the seven key principles
Purpose limitation
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the purpose must be documented and specified in privacy information that is communicated to the individual
data must not be used for a new purpose unless they are compatible with the original purpose. If it is not then additional consent must be obtained unless there is a clear function or obligation set out in law
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storage limitation
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There must be a periodic review of the data held, and data no longer required should be erased or anonymised
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data can be kept for longer if it is only kept for public interest archiving, scientific or historical research, or statistical purposes
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accountability
the data holder must take responsibility for how the data is used and for compliance with the other principles
Lawfulness, fairness and transparency
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Copyright, designs and patents act 1988
The CDPA protects the intellectual property of a individual or organisation. Under the act it is illegal to copy, modify or distribute software or any other intellectual property without the relevant permission. This act also covers video and audio where peer-to-peer streaming has had a significant impact on the income on the income of the copyright owners. Using the internet to download free copies of copyright material (software,films,books,music) without the consent of the autor is illegal since no money or credit will have been passed to the original creator.
Software licences
Most commercial software will come with a licence agreement specifying how the purchaser may use the product. In most cases a licence key will be required to access the software to prevent unauthorised copying and distribution
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Logic gates
AND gate
an AND gate uses two inputs to generate one output. The output is 1 (TRUE) only if both of the inputs are 1 (TRUE)
OR gate
an OR gate uses two inputs to generate one output. The input is 1 (TRUE) only if either r both of the inputs are 1 (TRUE)
NOT gate
a NOT gate uses just one input to generate one output. a NOT gate inverts the input - the output is 1 (TRUE) if the input is 0 (FALSE)
Compression
Lossless-Compression that doesn't lose any of the file's original quality is known as lossless compression. Lossless compression looks for patterns in the data. When it finds repeating patterns in the data, it takes the pattern and stores how many times the pattern occurs. An common example of this is 'zip' files.
Lossy-Lossy compression involves removing some of the data from a digital file in order to reduce its size. Lossy compression often reduces file size better than lossless but, once a file has been compressed using lossy compression, the lost data cannot be retrieved.
In the lossy compression of a sound file for example, the data removed might be sounds that the human ear is unable to hear, making the loss of quality as small as possible. This type of compression is often used for images, videos and music and is very helpful when streaming and downloading files.
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CPU and RAM work together : when a program is loaded it is copied into RAM ,the CPU can then access both data and instructions : Data is transferred from secondary storage into RAM to be used by the CPU : Once data and instructions are in RAM they are then transferred to cache memory, in order to further improve data access speeds for the CPU
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Cache memory
cache memory works as temporary storage the CPU can access quickly. Stores instructions and data that are used repeatedly or likely to be required for the next operation
The larger the cache memory the more likely it is that the required data will already have been copied across from main memory. Cache memory is very expensive and while a mid -range laptop may have 8GB of RAM it is likely to have just a few KB of cache
The more data that can be stored in cache memory rather then main memory the faster and more efficient the process Data that is likely to be required will be transferred to cache ready to be used
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