Category Archives: 1. Computer Systems

1. Computer Systems, Computing Higher

Cache Memory

Today’s lesson was a bit of a race, it covered Cache memory, SRAM & DRAM.

Its important that you remember that Cache Memory is not the same as Internet Cache. If you can’t get your head around how me running back and forth to the filing cabinet was caching then have a look here.

As a by the way, we also learned today that a memory location can hold more that one bit. I wonder if that will be useful in the future?

1. Computer Systems, 2. Software Development, Homework, Revision

School closure

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Well the wind has picked up and we are off school. To prepare for tomorrow’s lesson you can read over the scholar section on computer structure we are working through. Remember, I have a useful report section that allows me to check who has read this and who has not.

You can also head over to revise computing and try their resources.

Finally, there are a few of you still to hand in this weeks programming homework, so you could finish that off.

Plenty to keep you busy and out of the weather, stay safe and I’ll see you tomorrow.

1. Computer Systems, Computing Higher

The Fetch Execute Cycle

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The Fetch Execute cycle (Memory read instruction)

  1. The memory address of the next instruction is placed on the address bus
  2. A read signal is activated on the read line
  3. The data stored at the memory address is placed on the data bus
  4. The processor interprets the instruction
  5. The processor executes the instruction

The Fetch Execute cycle (Memory write instruction)

  1. The required memory address is put in the Memory Address Register
  2. The value to be written is put into the Memory Data Register
  3. The control unit activates the Write Line.
  4. The contents of the Memory Data Register are transferred by the data bus to the required memory address.
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