Computer Science GCSE

Computer Science GCSE

1. Computer Systems

   • Systems Architecture
     • Von Neumann Architecture
       • Von Neumann architecture is based on the stored-program computer concept, where instruction data and program data are stored in the same memory
       • Procesors
         • Control Unit
           • Controls the operations by ALU, memory and input/output devices
             • How to respond what is read from memory unit
             • Timing, controls signals required by other components
         • Fetch-Execute
           • Registers- Store data, instructions, addresses on processor (temporary)
             • Fastest access time of any storage location as in processor
             • MAR
               • - Memory address Register: holds address of next item of data needed by the processor
             • MDR
               • -Memory Data Register: holds the data that has just been passed by the data bus or has just been received from the data bus
             • ACC
               • -Accumulator: where the immediate arithmetic and logic results are stored (accumulates calculations), if no accumulator was present, CPU would store calculations on main memory and would have to retrieve the data from there, much slower
             • PC/CIR
               • -Program Counter: holds the address of the next instruction to be carried out, indicates where the CPU is up to in the sequence (counts)
               • Alternative Names: Instruction Pointer (IP) Instruction Address Register (IAR) Other Similar Registers: Current Instruction Register (CIR)- holds the address of the current instruction being processed
         • Accesses Memory Locations to read/write data
         • Quad-Core Processors- the more processors, the greater number of tasks that can be performed simultaneously (Octa-Core fastest)
         • ALU
           • Arithmetic
           • Logic (Gates)
       • CPU
         • Electric Circuit responsible for executing the instructions
       • Buses
         • Transmits and connects data with components
           • Address Bus
             • Carries the addresses of data (but not the data) between the processor and memory
           • Data Bus
             • Carries data between the processor, the memory unit and the input/output devices
           • Control Bus
             • Carries control signals/commands from the CPU (and status signals from other devices) in order to control and coordinate all the activities within the computer
       • Memory Unit
         • RAM
           • Volatile
           • Fast
         • Primary/Main Memory
         • Direct Access to CPU
   • Memory
   • Storage
   • Wired and Wireless Networks
   • Network Topologies, protocols and layers
   • System Security
   • System Software
   • Ethical, Legal, Cultural and Environmental Concerns

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