Notes from year 11

Notes from year 11

1. Data Representation

   • ASCII
     • The original ASCII only uses 7-bit numbers to represent the letters, numerals and common punctuation used in the English language. Each of those 128 values is assigned to a character.
   • extended ASCII
     • ASCII works fine for English strings such as ‘Hello World’, but what if we want to store a German string such as: ‘Es gefällt mir nicht’ (translates as: I do not like it). Basically we can’t use ASCII for this. So it was decided that as ASCII had an extra bit which was not in use, if ASCII was made into an 8-bit code rather than 7, it could store another 128 values. This system is called extended ASCII.

2. Von Neumann

   • A von Neumann-based computer: uses one memory for both instructions and data cannot distinguish between data and instructions in a memory location executes programs by doing one instruction after the next in a serial manner using a fetch–decode–execute cycle.
   • Advantages
     • The main advantage is that it simplifies the micro-controller chip design because only one memory is accessed. In micro-controllers, the most important thing is the contents of RAM (random-access memory) and in the von Neumann system it can be used for both variable (data) storage and program instruction storage. Another advantage is that it allows greater flexibility in developing software, particularly in the development of operating systems.
   • Disadvantages
     • Whilst the advantages far outweigh the disadvantages, the problem is that there is only one bus (pathway) connecting the memory and the processor so only one instruction or data item can be fetched at a time. This means the processor may have to wait longer for the data/instruction to arrive. This is referred to as the von Neumann bottleneck. The above reason can also lead to a system crash as there may be confusion between data and instructions.

3. Algorithms

   • An Algorithm is a set of instruction to help you complete a task (like a recipe) in a financed amount of time
   • An input stage represents the flow of data into the process from outside the system. An output is the stage where the data and the information flows out of the transformer. The processing stage includes all tasks required to effect the transformer to the inputs The feedback checks if the output is correct and tells the system to check the processor

4. Pen Testing