March 5, 2013

6502 Processor Facts

Filed under: Uncategorized — emmalaaaaawrence @ 10:55 pm
  • The first 6502 microprocessor was designed by Chuck Peddle and Bill Mensch in 1975 for MOS Technology.
  • 6502 is a low cost full-featured microprocessor.
  • The first development board of 6502 processor launched to the market was MDT-650.
  • One of the first publicly marketed computers using the 6502 technology was the Apple I computer in 1976.
  • The first video game console which uses 6502 technology was the Atari 2600.
  •  6502 is still made for embedded systems and video game consoles.
  • A 6502 processor is 8-bit processor.
  • It has only a few internal registers that allow addressing 64Kb of memory.
  • Clock speed of a 6502 processor: 1Mz or 2Mz.

The picture below is the circuit of the 6502.

September 9, 2012

Test Strategies and Changeover Strategies

Filed under: Uncategorized — emmalaaaaawrence @ 9:59 pm

Test Strategies

Black Box testing is a method that tests the functionality of an application. It doesn’t check the actual code, it checks the outputs are correct depending on the inputs.

White Box testing is like the opposite to Black Box testing. It tests the actual code of the program.



Changeover Strategies

Parallel Conversion: the new system and the old system are run side-by-side for a period of time to make sure nothing goes wrong and there is always a back up.

Phased Conversion: both systems run but gradually the old system stops in sections as the new system works and takes over.

Pilot Conversion: the old system still runs and people test that the new system produces the correct outputs and if it does then the new system takes over, if not it is edited until it is correct.

Direct Conversion: the old system is completely shut down and the new system is fired up.

Combined Conversion: this is a mix of the above, depending on the project.


Advantages and Disadvantages

September 6, 2012

System Design

Filed under: Uncategorized — emmalaaaaawrence @ 10:38 pm

Structure Charts

A structure chart is a hierarchy chart of individual steps in design. Each box/step is in the chart with arrows showing the flow of data and control information between them.

Data Flow Diagrams

Data flow diagrams use inputs and outputs to illustrate how data is processed.

Jackson Structured Programming

Jackson Structured Programming (JSP) is a way of structuring programs. It structures programs and data in terms of sequences, iterations and selections. It is similar to structure charts as each step is in a box and linked.


Pseudocode is made up of short English phrases that explain specific tasks that match to the program’s algorithm.

September 4, 2012

Info Systems

Filed under: Uncategorized — emmalaaaaawrence @ 11:07 am

Entity Relationship diagrams

An entity is a thing that represents a person or an object. It has a set of attributes that give information about the entity. The name of the entity is written in capitals and in singular form with a bracketed list following of the attributes.



There are three types of relationship:

1. one-to-one (1:1)

2. one-to-many (1:m)

3. many-to-many (m:n)




Each entity in the data model becomes a table in the database and each attribute becomes a field.



Data Dictionary

A data dictionary is a list of information about the data in a database, stored in a document.

August 16, 2012

What I Have Learnt

Filed under: Uncategorized — emmalaaaaawrence @ 2:16 pm
  1. Anomolies occur in flat-file databases.(insertion, deletion and update)
  2. An entity is a thing, attributes are information about the thing.
  3. You can filter databases and search them.

March 21, 2012

Bitmapped Graphics

Filed under: Uncategorized — emmalaaaaawrence @ 11:12 pm

There is two different devices that capture images. They are digital camera and a scanner, they use CCD’s to capture the images. CCD stands for Charged Coupled Devices, which are specially made integrated circuits that respond to light. These are connected to the computer and so an analogue to digital convertor (ADC) is needed as the computer only understands digital information whereas, the images are light (analogue) signals.

There are four main image file formats that store data as bitmapped graphics. This means they store information on the colour and placement of each pixel. The formats are:

  • Bitmap
  • Joint Pictures Expert Group
  • Portable Network Graphics
  • Graphic Interchange Format


Each pixel has a colour which is compared to colours within a table(CLUT – colour look-up table) and then replaced with a combination to represent it instead. This takes up less memory to store. Each pixel uses 24 bits (3 bytes) to store the colour. This is split into 3 different sections(RGB – Red Green Blue). The first 8 bits store the red value, second stores the green and the last the blue.

There is important formulas to remember for calculating file size, number of colours and number of pixels in an image.

No. of pixels = width of image x resolution x height of image x resolution

No. of colours = 2^bit depth

File size(bytes) = total no. of pixels x colour depth per pixel / 8


There is many different things you can do to an image to edit it. For example, you can crop it which cuts out some of the picture and makes it smaller. You could also perform dithering on it. Dithering is the process of placing two pixels, of different colours, side by side to create an illusion of a third color being present. This creates a cool pattern!

Another thing that you will need, to output the image, is a Graphics Card. Most come with their own processors these days as they carry out a lot of instructions. They also come with Video RAM memory which is physically closer to the processor on the card, which will make processes happen quicker.

January 8, 2012


Filed under: Uncategorized — emmalaaaaawrence @ 5:30 pm

Over the Christmas holidays, I set time aside to completely focus and revise on the computing course. The prelim for computing is on Monday 30th of January and so there is a short time period for studying. Over the holidays I have tried to equally study all five of my subjects. I did a total of about 5 hours of revision and will be doing much more. I tried to focus on the new parts of the course as last year   studied intermediate 2 and the course is similar. I took my own notes from the slide shows that Mr Cunningham made and I also used a helpful book that my brothers had when they studied higher computing. I didn’t feel the need to focus too much on binary as I feel quite confident in that area with data representation of text, real numbers etc. I also used the flashcards provided on the wiki and tried to learn them all in order to achieve over 75% in the quiz after. I manged to get 90% which is a A- and feel quite happy and confident about the software development vocabulary.

December 7, 2011

Computer memory and addressibility

Filed under: Uncategorized — emmalaaaaawrence @ 10:44 pm


This is the name of the process of identifying a memory location. Each location has a unique address so they can be accessed. The amount of locations depends on the width of the address bus or the number of lines within. To work out the amount of locations, you do 2^(number of bits in address bus). For example, an 8 bit memory address bus will be 2^8 which equals 256 accessible locations.

However, to calculate addressable memory, we need to know the amount of bits used to store the data in each location. This is the width of the data bus, or how many lines it has.

The formula to remember:

  Total addressable memory = number of storage locations x size of each location

Computer Memory

Memory comes in various ways. You have main memory(primary) which is held on chips and secondary memory is the backing storage. There is also RAM which stands for Random Access Memory. It can hold the processor and applications but when the computer is powered off, everything stored in RAM is lost. There is other versions of RAM, which are SRAM and DRAM(Static RAM and Dynamic RAM). SRAM is faster to access things but DRAM is what is used to make up RAM as it needs less power to work  and its easier. ROM(Read Only Memory), this holds the bootstrap loader and keeps everything stored in it when the power is turned off. Also different types of ROM, they are PROM, EPROM,EEPROM.

However, reading and writing to and from RAM causes the system to slow down. So, we get cache memory. This is between the processor and main memory so it is quicker to access. It stores instructions it thinks you may want carried out so everything is faster. We can also store things in registers, for example the Memory Address Register holds the data being processed. Registers are even faster than Cache.

Back to the backing storage, some of its memory is set aside and called virtual memory. This area of the hard disk is used to store things temporarily but it has its disadvantages as it is slower to access.

November 28, 2011

The Processor

Filed under: Uncategorized — emmalaaaaawrence @ 9:40 pm

The processor is the main part of the computer. It can perform one task at one time. It is found in the centre of the Von Neumann Architecture(a diagram showing inputs, outputs, main memory and backing storage).

Inside the processor there are different areas: control unit, ALU, MAR, MDR and other registers.

The control unit is the part in charge of information like performing actions. The ALU stands for Arithmetic and Logic Unit, this is the part that does the calculations, it is the brain of the computer. MAR stands for Memory Address Register and MDR stands for Memory Data Register. These are very fast, temporary storage locations that can store things like addresses of memory locations and instructions. Other registers are very similar.

Buses are used to pass information within the processor and to main memory. The main buses are the address bus, data bus and control bus.

The address bus carries information from the memory address register to main memory. Within main memory, there is many unique locations, the information from the address register tells main memory which specific location is going to be read or written to. Inside the bus there are many wires, each wire can carry one piece of information. The more wires, the larger available memory locations.

The data bus is different as it can carry information from the memory data register to the main memory and vice versa. It can store information in the unique address and read from the location too. Increasing the width of these buses means that more data can be carried at once so the computers performance is better.

In the control bus, each wire does a different thing. The five main wires are: Read, Write, Clock, Reset and Interrupt.

November 4, 2011

Bitmapped Graphics

Filed under: Uncategorized — emmalaaaaawrence @ 10:26 am

Images are made up of hundreds of tiny dots known as pixels. The higher amount of pixels, the better the picture, this is called the resolution. If there is a small number of large pixels then the image will be blurry and unfocused.

We use binary to represent the colour in pixels. Each pixel is represented by the same amount of bits, for black and white images.. we use 1 bit. 0 represents white and 1 represents black.

For coloured images, we have to use more bits to store each pixel.

For example, if we wanted to have four colours, we would use 2 bits. We would store them as 00, 01, 10 and 11. These can be ANY four colours. For 8 colours we use 3 bits and for 16 we use 4 bits. The amount of bits used to represent each colour of the pixel is called the bit depth.

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