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Monthly Archives: November 2011

The Processor

This week in computing, our class learnt about the processor. Within the processor, there are the control unit, ALU, MAR, MDR and Registers.

Von Neumann Architecture.


Inside the Processor

ALU: This is the arithmetic and logic unit. This part of the processor carries out all the arithmetic calculations and logical operations (AND, OR, NOT) the computer is asked to do.

Control Unit: This part of the processor controls the fetching and executing of instructions. It keeps everything synchronised and manages the reading and writing to and from the main memory. #

General purpose registers: These are very fast temporary storage locations on the processor.

MAR: The Memory Address Register is the register which holds the unique storage location of what piece of information is needed from the main memory

MDR: The Memory Data Register is the register which the information from the main memory is retrieved and also where it is sent back to the main memory if it is re-written or slightly changed.

Buses: These are physical wires which connect each part of the processor together.

The Control Bus

Each wire on the control bus has its own separate function. There are five:

Read Line: This informs the memory that data has been sent to the processor from a particular memory location.

Write Line: It informs the memory that data is to be written to a specific memory location.

Interrupt: A message which is received from a peripheral device causes the processor to stop doing the current task and deal with the message from the peripheral. Current data is stored into a temporary storage location on the processor called the stack. The processor then deals with the interrupt and once the task has done, it retrieves the data from the stack and carries on with the task.

Clock: This line keeps everything synchronised. It generates a steady pulse which keeps the flow of information constant.

Reset: This line clears all the internal processor registers and switches the computer back to its original switched on state.


 
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Posted by on November 29, 2011 in Computing

 

bitmapped graphics

Pictures which are viewed on digital devices are made up of pixels(picture elements). A pixel is the smallest unit of picture which can be controlled.Pixels are normally arranged in a two-dimensional grid and are often represented by dots or squares. To represent a black and white image, it will be stored in 2 bits, 1 being black and 0 being white. Although what would happen if the picture was in colour? It would be stored using more bits per pixel.

The resolution determines the quality of the image. So the smaller the pixels the greater the resolution.

There are two types of graphic, bitmapped and vector.

Bitmapped Graphics.
Bitmapped graphics are stored in a two dimensional grid (array) using binary to represent the colours of the pixels. Each pixel is represented by the same number of bits.

For black and white, each pixel is represented by one bit. Black = 1 and white = 1.

For colour, each pixel will be represented by the amount of bits required. For example, if there are four colours (black, white, red and green), each pixel would be represented as 2 bits.

00 = Black

01 = White

10 =  Red

11 = Green

Vector Graphics

Vector graphics  are objects such as geometrical shapes which are stored as mathematical equations which contain attributes of how they are to be drawn.

The computer will automatically save the new attributes if the object if :

-it is moved around the screen

-it is resized

– the fill pattern is changed

-the line thickness is changed

When using vector graphics, it is not possible to change the colour if the object or delete part of the object.

 

 
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Posted by on November 7, 2011 in Computing

 

Representing Real Numbers

In representing real numbers, computers are programmed to use Floating Point Representation. In floating point represnetation, the real number is stored as two seperate pieces of data, called the mantissa and exponent.

The mantissa holds the complete number without the point.

The exponent holds the amount of places the point needs to be moved to the left hand side to keep the original number.

Example:

What is the mantissa and exponent of 011010.01?

The mantissa would be: 01101001

The exponent would be: 6 (0110) as the decimal point needs to be moved 6 places until it gets to the far left-hand side.

=> 01101001 x2^0110

although it is not necessary to store the base 2 or the”x” sign as they will always be involved.

Accuracy in real numbers.

If the mantissa is onlt storing 8 bits for the whole number and the number is nore than 8 then some of the numbers after the point will have to be discarded, therefore the accuracy of the number will be decreased

Example:

Ifthe binary number is: 0110100.1001

it will have to be reduced to 0110100.1 as the mantissa can only hold 8 bits, decreasing the accuracy.

Range.

Increasing the range of the mantissa and exponent allows the number to have more accuracy and a larger range of numbers which it could be.

Representing Negative Numbers.

There are two ways to represent negative numbers. a theoretical way is called signed bit represtentation. This is when the computer would take the leftmost bit of the number and assign a positive or negative sign but this is not used as there is two values for zero. So two’s compliment represetation is used.

When using twos compliment, all the zeros in the binary number must be changed to a one and all the ones must be changed to a zero. Then a one is added on.

Example.

What is negative 5?

firstly what is 5 in binary? 0101-> 1010

1010

  +1

= 1011 -> negative 5

 
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Posted by on November 5, 2011 in Computing