Thinking Ahead


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CPU Fetch-Decode-Execute Cycle

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A CPU (central processing unit) executes and manages the rest of the hardware inside a computer system - it is the brain of a computer! The CPU is made up of the main memory, the processor and the cache memory. It's job is to process data (by processing we mean searching, sorting, calculating and decision making). The CPU follows the Fetch-Decode-Execute cycle. The Fetch Stage: the CPU use a piece of hardware called the ' address bus ', this is where the CPU asks the RAM for some data. The RAM then responds with this data on the ' Data Bus '.  The Decode Stage: This is where the CPU converts the instructions in to a way in which it understands it. It then gets things ready for the next step.  The Execute Stage: This is where data processing happens. Instructions are carried out on the data, as soon as the command is completed it starts the next one. 
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Types of Switching (Data Transmission)

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Circuit Switching Creates a direct link between two devices for the duration of communication. Example is a telephone system. If you are calling somebody on your mobile and somebody tries to ring you they will get a 'user is unavailable message'. This is because when a call is made a direct path in a telephone exchange is made by various switches. Advantages of this is that it is quick (no delay) as there is no interference and also the fact that it is simple to set up. Only two people are using the connection at once, everyone else would be rejected. Disadvantage is that only one connection can be made at once, group calls are multiple calls on one line aren't possible. Also it wastes a lot of bandwidth, even if a person is on hold the line is still in use/data being sent so no one else could use it. It is important with Circuit Switching that data is sent/received at the same rate otherwise there will be delays/pauses in the call. Data always arrives in the ord...
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OSI Network Model

Open Systems Interconnection (OSI) model - a conceptual framework that describes the functions of a networking or telecommunication system. The OSI model has 7 layers.  Layer 7 - Application Layer This is what the user communicates with. It is the applications that we used - Google Chrome & Skype are examples.  Layer 6 - Presentation  This is where data is converted from the application framework into something that the network understand. The data would be encrypted here for example.  Layer 5 - Session Computer need to create a session between the two devices so they can speak to each other. This is done here. The computer communicate telling each other how much time they should wait for a response from each other and what they should do when the task has been completed (end session) etc.  Layer 4 - Transport  The Transport Layer deals with the coordination of the data transfer between end systems and hosts. This...
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