Computing Revision

Binary Logic
1. Data is represented in computers in binary form as binary code is made up from ones and zeroes and the computer system can only understand ones and zeroes so other programming languages would be unreadable to the computer without it being changed into binary.
2. AND gate
  1. In an AND gate, both A and B need to be input for an output to be recieved
3. OR gate
  1. In an OR gate, only one input is needed to recieve output, but more than one makes no difference.
4. NOT gate
  1. In a NOT gate, If there is input no output is recieved, and if there is no input output is recieved. (Check note attatched)
    Annotations:
    - NOT Logic Gate truth table: Input Output 0 1 1 0
Number
1. An 8-bit binary number such as 11001011 can be converted easily into a positive denary whole number, you can use a table to work out how to convert Binary-Denary and Denary-Binary. (Check note attatched)
  Annotations:
  - 11001011 would become 203 using this table: 128 64 32 16 8 4 2 1 1 1 0 0 1 0 1 1 Even though they both seem to be the same, the left-most 1 is equal to 128 in denary and the right-most 1 is equal only to 1
2. Adding binary numbers. (See note attatched)
  Annotations:
  - Let's try adding 0111 and 1110: 1 1 0111 (Start at right) 1110 (1+0=1) 10101 (1+1=2, which is 10) (Carry the one over)
  - The number ended up being 5 bits, if it had to be only 4 then the one being carried left would have caused an overflow which can be a problem.
3. In order to convert binary into hexadecimal you need to break it down into nibbles so 10001101 would be 1000 and 1101, in denary 1000 is 8 and 1101 is 13, using the table above, we know 13 in hexadecimal is D and 141 would be 8D
4. It is much easier to work with binary through hexadecimal
Units
1. Bit - Unit of information (1 or 0)
2. Byte - A group of 8 Bits operated on as a unit
3. Nibble - 4 Bits (Half a Byte)
4. Kilobyte - 1024 Bytes
5. Megabyte - 1024 Kilobytes
6. Gigabyte - 1024 Megabytes
7. Terabyte - 1024 Gigabytes
8. Data such as programming code cannot be read by the central processing unit of a computer so must be converted into binary code so it can read the instructions.
Character
1. We use code to represent characters as it is much easier to understand 'John' than it is to understand 01001010 01001111 01001000 01001110
2. A character set is a list of characters recognized by the computer software and hardware, each character being represented by a number
3. Each character in the ASCII character set is 7 bits and a total of 127 different characters are accesible, whereas Unicode characters are 16 bit and over 110000 characters are available
Images
1. In an image, each pixel has a colour which can vary depending on the binary number assigned to it and the amount of bits are in each number as the more bits available, the more colours and greater colour depth accessible.
2. The metadata of an image is very important as it contains important information about the image such as resolution, dimensions and colour depth, without these the picture will not load.
3. An image with a high resolution or massive colour depth will have a much larger file size meaning it will take up more room and will require more time to load
Sound
1. Sound can be sampled and stored in digital form using an analogue-to-digital converter, the quality of this digital sound depends on the sample rate as a high sample rate will result in a clear sound but will take up more memory.
Instructions
1. Every central processing unit is made up of machine code instructions which are patterns of ones and zeroes, these are stored in the computer's random access memory.
2. The cpu uses opcode to determine which of the upcoming bytes from the data bus are data
Computer Systems
1. Software means the programs, including both the operating system and any application software, such as spreadsheet or presentation software.
  1. Do not say Word, PowerPoint or Windows. Instead, say word-processing software, presentation software or operating system.
2. Hardware means the physical components such as a keyboard, mouse, monitor, hard disk, printer, scanner, webcam or anything else you can touch.
3. Input devices are used to put data into the computer. Keyboards, mice and webcams are examples of input devices.
4. Output devices allow data to be sent beyond the computer, usually to a human user. Monitors, speakers and printers are examples of output devices.
5. Storage devices are used to contain programs and data. USB flash drives, DVD drives and internal hard disk drives are examples of storage devices.
6. Computer systems do not all look like computers, some are embedded. An embedded system is a computer integrated into another device, such as a mobile phone, washing machine, petrol pump or television.
Professional Standards
1. Any computer system is the result of collaboration between large numbers of people, often working completely independently in several countries. For this arrangement to work, professional standards are essentially rules that everyone follows in developing computer systems, rather than everyone doing their own thing. A very basic example of this is USB ports and cables; many manufacturers produce them separately, but they all produce them to the same specifications, or they wouldnt fit.
2. Professional standards exist in software as well as hardware, and there are several in programming
3. The reason these standards are followed is that another programmer, possibly without ever meeting the original programmer, might be expected to make changes to this program or write another program that interacts with it.
  1. Professional standards allow programmers to do the following:  Modify someone else's program  Move to a different company without needing to re-learn these standards  Work in teams on the same program at the same time
    1. Professional standards fall into four categories
Ethical, Environmental and Legal Considerations
1. Ethical
  1. The word 'ethical' refers to something as being right or wrong, although not everyone agrees about what is right and what is wrong, even in something as specific as computing. Consider the following:  Would it be ethical (right) for a government to store an electronic profile of the DNA of its entire population, of criminals, immigrants, etc.?  Is it ethical to use cheap labour in foreign countries to produce software less expensively, or would it be more ethical to use local labour?  What are the ethical challenges of living in a world where not everyone has access to computers, either for financial-, political- or disability-related reasons?
2. Legal
  1. There are four laws that computer users need to be aware of:  Computer Misuse Act This makes hacking illegal. Hacking is gaining access to computer material that you are not allowed to have access to, possibly by stealing a password.  Data Protection Act If you (or the company you work for) store the personal data of anyone, you are required to keep it secure and up to date.  Copyrights, Designs and Patents Act It is illegal to make a copy of any publication (including written works, music and computer programs) without the permission of the copyright owner.  Health and Safety at Work Act This law makes employees responsible for the safety of their staff, as well as staff responsible for the safety of other staff. In terms of computers, the following are considerations:  Trailing cables that are a trip hazard  Too much time spent at a computer which can cause eye strain from looking at the screen or repetitive strain injury (RSI) from typing or using the mouse
3. Environmental

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	Created by masterjriddoch about 10 years ago