Data Representation

Number
1. convert positive denary whole numbers (0-255) into 8-bit binary numbers and vice versa
  1. diagram
2. two 8-bit binary integers and explain overflow errors which may occur
  1. both numbers are small enough to fit within 8 bits, but when they're added together, they 'overflow' into 9 integers, and will not fit within 8 bits.
3. convert positive denary whole numbers (0-255) into 2-digit hexadecimal numbers and vice versa
  1. diagram
4. convert between binary and hexadecimal equivalents of the same number
  1. diagram
Units
1. Bit = a single binary digit
2. Nibble = a sequence of 4 bits
3. Byte = a sequence of 8 bits
4. Kilobyte = approximately 1000 bytes
5. Megabyte = about 1000 kilobytes or 1,000,000 (one million) bytes
6. Gigabyte = about 1000 megabytes or 1,000,000,000 (one billion bytes)
7. Terabyte = approx. 1000 gigabytes or 1,000,000,000,000 (one trillion) bytes
8. Data needs to be converted into binary to be processed by a computer, that is why this information is a necessity to know.
Binary logic
1. Why is data in computers represented in binary form?
  1. Computer componentts often have two states that can easily model 1 and 0. A magnet on a hard disk can either be aligned north or south and a circuit cam be either open or closed.
  2. Binary is high tolerance, it is unlikely that a computer could mistake a 1 for a 0, in the same way that a computer could easily mistake a 4.26 for 4.27 if, say, a computer used different voltages to represent more than 2 numbers.
2. Logic gates
  1. NOT
  2. OR
  3. AND
3. Example of a logic gate w/ truth table
Characters
1. A character set is a defined list of characters recognized by the computer hardware and software. Each character is represented by a number. The ASCII character set, for example, uses the numbers 0 through 127 to represent all English characters as well as special control characters. European ISO character sets are similar to ASCII, but they contain additional characters for European languages.
2. ASCII
  1. When using the seven bits-per-character setting, it is possible to only send the first 128 characters (0-127) of the Standard ASCII character set. Each of these characters is represented by seven data bits. The eight bits-per-character setting must be used to send the ASCII Extended character set (128-255). Each of these characters may only be represented using eight data bits.
3. Unicode
  1. As opposed to ASCII, which only contains a maximum of 7 or 8 bits per character, Unicode contains 16 bits, or 2 bytes!
4. There is a table in computer (used by BIOS) tells which byte what symbol represents. When you press a key (for example "A"), keyboard interrupt is fired and BIOS or Operating System reads one byte (0x41) from keyboard buffer. After that BIOS or Operating System is asked to write in on keyboard buffer. After that BIOS or Operating System is asked to write in on screen. Because we tell them to draw a character on the screen they look on the table to check the entry for (0x41) in ASCII table and it writes that information to video buffer. After screen is refreshed we see "A" character on he screen. The entry of table will tell what pixels in some predefined square of screen should be colored white and which black.
Images
1. The more colour depth an image has and the higher the resolution of an image, the larger the size of an image file.
2. Simply put, metadata is data about data. It is descriptive information about a particular data set, object, or resource, including how it is formatted, and when and by whom it was collected.
  1. It is necessary because it helps to support archiving and preservation. Provenance information, such as height, width, and colour depth, aids the long term preservation of repository content.
3. All bitmap images are stored as an array of pixels. A monochrome bitmap will store a 1 for a black pixel and 0 for a white pixel (or vice-versa depending on the encoding protocol). If the image were in colour, using a colour palette of 256 possible shades, each pixel would need to translate to a value between 0 and 256 (8 bits). Thus we would need 35 bytes to store the image. It is common for colours to be recorded by quantity or Red, Green and Blue (RGB) and this is stored using 3 bytes per pixel – so we would need 105 bytes to store the image.
Sound
1. In order to store sound digitally, the voltage is sampled at frequent intervals (typically 48 000 times per second, or 48kHz) and stored as a binary code (typically 16 or 32 bits per sample).
2. Diagram of sampling
3. Sample Rate: By reducing the sample rate (e.g. to 22kHz), you reduce the amount of data you need to store. This has quite serious effects on the quality of the audio.
4. Sample Depth: Much as with colour, you can reduce the precision of each datum, using only 8 bits per sample instead of 32, for example.
Instructions
1. Our CPU processes instructions and data. It receives orders from the software. The CPU is fed a gentle stream of binary data via the RAM. These instructions can also be called program code. They include the commands which you constantly – via user programs – send to your PC using your keyboard and mouse. Commands to print, save, open, etc. Data is typically user data. Think about that email you are writing. The actual contents (the text, the letters) is user data. But when you and your software say “send”, your are sending program code (instructions) to the processor:
2. Even the incredibly simple microprocessorwill have a fairly large set of instructions that it can perform. The collection of instructions is implemented as bit patterns, each one of which has a different meaning when loaded into the instruction register.
3. Humans are not particularly good at remembering bit patterns, so a set of short words are defined to represent the different bit patterns. This collection of words are called the assembly language of the processor. An assembler can translate the words into their bit patterns very easily, and then the output of the assembler is placed in memory for the microprocessor to execute.

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	Created by joem1998 about 11 years ago