This weeks blog post is on describing some of the aspects of bitmapped graphics that I have learned. 

There are 2 main types of input hardware devices used for capturing still graphic data. These are a digital camera and a scanner. Digital cameras and scanners both use charged coupled devices – or CCDs – to capture data. ADC stands for analogue to digital converter. Digital cameras and scanners require analogue to digital conversion to convert light signals to digital signals. 

There are 4 main types of storing graphic data – Bitmap (BMP), Graphic Interchange Format (GIF), Joint Pictures Expert Group (JPEG) and Portable Network Graphics (PNG).

There are 2 types of compression – lossy and lossless. Lossy means that you lose quality when saving the image.

Resolution is the term given to the amount of dots per inch. The formula used to calculate the resolution is:  Number of pixels = image width x resolution x image height x resolution.

RTF and TXT are different ways of saving a word document. An RTF is more powerful than a TXT, it has more presentational value. TXT files cannot retain any sort of formatting. Although some text editors may be able to change the font, size and other aspects, all the changes will be lost once you save it into a TXT file. With RTF, you can create paragraphs and move the writing to the left right or centre. When saved as an RTF file this will remain however if saved as a TXT file, these changes will disappear. Another difference is that RTF files are able to contain images, however TXT files are not.

Over Christmas I have been very busy but obviously managed to do some revision and all my homework. In total I have probably done about 4/5 hours which might not seem a lot but when you have 4 other subjects and a busy social life then its alright :). I have revised a lot of the software development process and programming languages.  I also read over most of the notes on data representation and binary.

Computer addressability: 

Addressability is the way in which the computer identifies different memory locations. Each memory location has a unique address, meaning it is one of a kind.

Memory:

There are 2 main types of memory:

  • Main memory (aka primary memory) is held on chips. 
  •  Backing storage (aka secondary memory) is not part of the computers main memory.

The size/width of the address bus determines how many memory locations can be accessed.  For example –  a 1 bit address bus can access 2 memory locations,  a 2 bit address bus can access 4 memory locations and a 3 bit address bus can access 8 memory locations etc.

To calculate the total addressable memory of a computer, use this equation:

The number of storage locations x the size of each storage location

Each storage location holds one word.

There are 5 main types of memory:

  • RAM
  • ROM
  • Cache
  • Registers
  • Virtual

There are 3 types of  ROM memory:

  • Programmable ROM (PROM) –  This type of ROM has no pre-written data on it and is empty so that the user can program it, however, once written, the data cannot be erased.
  • Erasable PROM (EPROM) – This is the same as PROM except it can be removed from the computer, have it’s data erased and have another put in it’s place using Ultra-Violet light.
  • Electrically EPROM (EEPROM) – The same as EPROM except electricity is used to erase and re-write selected contents.

There are 2 types of RAM memory; Static RAM (SROM) and Dynamic RAM (DRAM). SRAM has faster access speeds than DRAM, however the processor mainly uses DRAM as it is more simple to use and it also uses less power.

Cache memory is physically built into the processor, which is placed closer to the processor than RAM. This memory is used to store the next instructions which are going to be read by the computer.

This week’s blog post was to be about the processor. This was to include things such as Von Neumann architecture, ALU, Control Unit, Registers, Buses, MAR and MDR.

The Von Neumann architecture has 5 main parts – the processor, the input devices, the backing storage, the main memory and the output devices.

The arithmetic and logic unit carries out all calculations and perform logical operations, for example or, not, and.

The  control unit manages the fetching, decoding, and executing of all instructions.

The  registers are a very fast temporary storage location which holds: the data being processed, instructions being executed and the addresses of memory locations to be accessed. These registers are linked to buses.

Internal buses are used to transmit information. The address bus carries the information from the processor to the main memory. This tells the main memory which memory location will be read and used to  store it. Each wire on the bus can only carry 1 bit of information at a time. The number of wires determines the number of memory locations.

The data bus carries information from the processor to the main memory. This stores data and reads it from the memory location. Each wire on the bus can only carry 1 bit of information at a time. Increasing the width of the bus increases the quantity of data that can be carried at one time.

In representing real numbers, computers are programmed to use floating point representation. In floating point representation, the real number is stored in two separate parts – the mantissa and the exponent. 

The mantissa holds the complete number without the decimal point.

The exponent holds the number of places the decimal point has been moved by, in order to make sure the value of the number remains unchanged.

For Example:

What is the mantissa and exponent of  10110.110? 

The mantissa would be 10110110.

The exponent would be 5, as the decimal point has been moved 5 places. In binary this would be represented as 010. 

The fewer bits the exponent and mantissa represented to, the less accurate the number is.

An image is made up of loads of tiny little dots, called pixels. The resolution determines the quality of the picture, so the smaller the pixels, the higher the quality and detail of the picture. There are 2 types of graphics: bitmapped and vector. 

Bitmapped graphics use binary numbers to represent colours. 0 = white and 1=black. To add more colours, 2 bits are used to represent them, so now white=00, black=11, red=10 and blue=01. When using 3 bits, you can represent 8 numbers, including yellow, green and different shades of blue. In order to represent all colours, they must be represented to 24 bits.

Graphics can be edited to pixel level. Enlarging the image cause loss in the quality. Compression can be used to decrease the size of image files when transferring them onto disc.