Internal and External Hardware

Internal and External Hardware

1. Main Memory

   • ROM (Read Only Memory)
     • Also a storage method for data and instructions
       • BUT non voliatile (data not lost when machinine switched off)
       • Stores limited instructions relating to the set up of the computer
         • Stored in the BIOS (Basic input and output system)
     • You can not alter the data on ROM as it is read only.
     • There is ROM that you can alter however.
       • E.G Memory Stick
   • RAM (Random Access Memory)
     • Accessed very quickly
     • Volitile memory (clears memory when switched off)
     • Software stored here.
     • Series of chips on which data is stored.
     • Made up of cells.
       • Each contain either data or an instructions with a unique address/
       • Access to cell is via the unique address system. (these can be accessed randomly)
     • More RAM you have the more you can store and retrieve.
   • Stores data and instructions
   • Connected to the proccesor which Fetch-Decode-Execute each instruction.

2. Buses

   • Microscopic wires connecting processor to input output controllers.
   • Three types of buses
     • Data Buses.
       • This carries instructions and data back and forth between the processor and memory as you are using a program.
       • Carries data and instructions to and from the I/O controllers.
         • Can be BI-directional. (both ways)
           • More efficient.
         • Input/ Output Controllers.
     • Address Buses.
       • One way bus route.
         • Processor in to memory.-->
       • If instructions are executed the Address bus caries the memory address of the next instruction or data.
       • Used to access anything in memory, just not instructions.
       • Address bus: used to specify a physical address in memory so that data bus can access it.
     • Control Buses.
       • Bi directional.
         • Sends control signal to the registers, the data and address buses.
       • Lots of data flowing around the processor.
       • Job to ensure the correct data is travelling to the right place at the right time.
       • Involves synchronisation of signals.
       • Control buses: controls the flow of data between the processor and other parts of the computer.
   • Connects internal parts of the microprocesor also.

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