All posts by Mr Stratton

Computing teacher and a PT at Coltness High School.
1. Computer Systems, Computing Higher, Homework

Answers for Homework 7th Dec.

Give two reasons why computers use binary numbers to represent and store data.(2)
  • A two state system is easy to represent using electrical signals.
  • Fewer rules need to be built into the processor for arithmetic operations.
  • It is also easy to represent a two state system on storage devices, eg. CD-ROM
Represent 0111 0100 in decimal.(1)
  • 0 + 64 + 32 + 16 + 0 + 4 + 0 + 0= 116
Describe how graphics are stored using a bit-mapped package.(2)
  • A bit map is a grid of pixels.
  • Each pixel has a binary value representing its colour.
  • All pixels in the image are stored even if they have not been assigned a colour.
An image is 4 x 6 inches, has a resolution of 800 dpi and each pixel can display 65,536 different colours. Calculate the storage requirements of this image. Express your answer using suitable units. Show all working. (3)
  • (4×800)x(6×800)x16
  • =3200x4800x16 = 245760000 bits
  • /8 = 30720000 bytes / 1024 =
  • 30000 Kb / 1024 = 29.3 Mb

State two advantages of storing the above image as a vector graphic rather than a bit-map.(2)
  • The image can be resized without pixelation
  • The file size will be much smaller as only a description of how to draw the object is stored, not each pixel.
  • Individual objects can be edited without affecting the rest of the image (non-destructive editing)
Represent 13.25 in floating point notation.  Express the mantissa in 16-bits and the exponent in 8-bits.(2)
  • 1101.01
  • Mantissa = 1101 0100 0000 0000
  • Exponent = 0000 0100
  • 1101 0100 0000 0000 x 2 0000 0100
What is meant by the term lossless compression?(1)
  • File size of graphic is reduced without any visible reduction in graphic quality
Explain how the Unicode system overcomes the limitations of ASCII.(1)
  • Unicode uses 16-bits compared to ASCII’s 7-bit representation. This allows all the world’s character sets to be represented instead of just 128 characters.
How many different colours could be represented with a bit depth of one byte(1)
  • 1 byte = 8 bits
  • 28 = 256
  • 256 different colours can be represented
1. Computer Systems, Computing Higher, Revision

2’s Complement

Right I am adding the finishing touches to the revision powerpoint I promised you. However, while I was going over sign and magnitude, I came across this.

http://en.wikipedia.org/wiki/Signed_number_representations

“Useful” I hear you say, but there is more to this than meets the eye. There is on that page a method for converting a number to 2’s complement that I haven’t see in quite a while and I thought I might share it with you.

  1. Starting from the right, find the first ‘1’
  2. Invert all of the bits to the left of that one
So for 42 to convert it to -42
  1. 00101010
  2. 11010110
Computing Higher

Snow

2 Comments

Right so the snow is here, we knew it was coming. I have not changed any of my plans for the next few weeks leading up to the end of term.

Tuesdays will be NAB 2 of software development. I will hand out the task tomorrow and collect it in the last week of term, failure to hand it in will be a fail and a resit will be required.

Wednesday, Thursday and Fridays will be Computer Systems. Materials and slides will be posted for each day and will make use of scholar materials in the event of school closures.

An assessment will take place on the 16th, consisting of single past paper (with some questions removed).

Take care in the snow folks and check back often.

2. Software Development, Computing Higher, Homework

Homework for Wed 7th Dec

2 Comments
  1. Give two reasons why computers use binary numbers to represent and store data.(2)
  2. Represent 0111 0100 in decimal.(1)
  3. Describe how graphics are stored using a bit-mapped package.(2)
  4. An image is 4 x 6 inches, has a resolution of 800 dpi and each pixel can display 65,536 different colours. Calculate the storage requirements of this image. Express your answer using suitable units. Show all working. (3)
  5. State two advantages of storing the above image as a vector graphic rather than a bit-map.(2)
  6. Represent 13.25 in floating point notation.  Express the mantissa in 16-bits and the exponent in 8-bits.(2)
  7. What is meant by the term lossless compression?(1)
  8. Explain how the Unicode system overcomes the limitations of ASCII.(1)
  9. How many different colours could be represented with a bit depth of one byte(1)

Out of 15.