SLR 3

• Explain why all instructions and data used by a computer are represented in binary

  A processor consists of billions of transistors each of which have two states ON/OFF. The on/off states of a transistor represent the binary digits 0 and 1
• What is a 'bit'

  Short for binary digit. It's the smallest unit of data in a computer. A bit has a singular binary value which is either 0 or 1
• Why can the denary number 256 not be represented in an 8 bit binary pattern


  Because the denary number 256 would be represented as 1 0000 0000 in binary and so would need 9 bits to store it.
• What is one difference between a logical and an arithmetic shift

  An arithmetic keeps the leftmost sign (furthest bit left) the same. Essential for two's complement. Whereas the logical shift always fills in the vacated bits with 0's.
• Define the term overflow.

  An error that occurs when a calculation produces a result that is greater than the computer can store, or is greater than the number of bits available to store it.
• State two consequences of an overflow error.

  Program might crash. Further use of the incorrect results in calculation will cause further error.
• Why is Hexadecimal used?

  Hexadecimal is used because people get confused with large binary numbers. binary numbers can be simplified by writing them in Hexadecimal as fewer numbers/characters are needed
• Convert the binary number 1101 0101 into hexadecimal

  D5
• Convert the hexadecimal number BD into binary

  1011 1101
• What is meant by the character set of a computer?

  The lest of binary codes that can be recognised by the computer hardware/software
• How is ASCII used to represent characters in a computer system

  ASCII is 7-bit, which allows for 128 code sequences representing the english alphabet and control actions. The codes are group in terms of function.
• привет, меня зовут Сандра. Hello, my name is Sandra. Why can only the 2nd sentence be represented in ASCII

  The first sentences is made up of foreign characters, which do not fit into the 7-bit ASCII. While the 2nd sentence is made up of english characters so can therefore be represented in 7-bit ASCII.
• What is meant by the size of an image

  The number of pixels in it's width and height.
• What is meant by the resolution of an image

  the number of pixels per unit area of display
• What is the formula for the number of colours that can be represented with a given colour depth

  2 ^ n
• What is meant by sample rate

  The number of sound samples that are taken each second
• What is the effect of increasing the sample rate

  Gives a more accurate reproduction of the analogue waves, as more samples are taken with less time between them
• What is meant by 'bit depth of a recording'

  The number of bits used to encode the data taken in each sample.
• What are 4 factors that affect the size of a sound file

  The sample rate, bit depth, length of recording, number of channels
• State the formula used to determine the number of distinct binary patterns for a shown number of bits


  2^n
• Why may a lower amount of bits be the preferred way to store colour depth in an image.

  The higher colour depth file would take longer to transfer and load more slowly. The slight increase in quality with the higher colour bit depth may not be needed in application and may not matter to the person viewing it
• Why would the bit depth of an audio recording be reduced

  Reduces the file size, allows for a faster transmission. Reducing the bit depth, may also lower the distinct values, however these may not be noticed by the human ear.
• State the order of units of measurements for data storage

  Bit, nibble, byte, kibibyte, mebibyte, gibibyte, tebibyte.
• What are 3 advantages of compressing files

  Uses less internet bandwidth when sending and receiving, transfer speed is quicker, takes up less storage space
• Describe lossless compression

  Reduces file size without deleting any data. Lossless compression looks for redundant information and groups this data into one reference in the file. When the file is later decompressed, it is exactly the same as the original, nothing is lost.
• Describe lossy compression

  Reduces file size by deleting some data. The original can never be reconstituted after it's decompressed as it has been irreversibly changed.
• What compression would you use for a PDF file of a novel

  Lossless - the novel would be impossible to read if some of the data (words) are deleted
• What type of compression would you use for images from vacation

  Lossy - areas with similair colours can be merged together into one to reduce file size. People cannot distinguish between small differences in colour.