Systems Architecture

• A computer is an electronic device which takes input, processed data and delivers output
• The process of the CPU is to fetch, decode and execute
• Fetch is: fetching the next instruction from main memory (RAM) and bringing the instruction back to the CPU
• Decode is: inspecting the instruction and working out what needs doing
• Execute is: Carrying out the instruction e.g performing and calculation
• Arithmetic Logic Unit (ALU): performs calculations such as Logical operations (AND, NOT,OR) shift operations and arithmetic operations
• Control Unit (CU): sends signals to control how data moves around the CPU
• Cache: Fast access to frequently used instructions and data
• Registers: tiny super fast pieces of onboard memory inside the CPU each with a very specific purpose
• Program counter (CU): holds the address of the next instruction in memory
• Memory address register (MAR): holds the address of where data is to be fetched or stored
• Memory data register (MDR): holds data fetched from or to be written to memory
• Accumulator: Holds the result of calculations
• Von neumann architecture consists of: control unit, arithmetic logic unit, memory unit and inputs and outputs
• Von neuman architecture is based on the concept of the stored-program concept
• In the von neuman architecture both instructions and data and program data are stored in the same memory in binary form
• There is no way to know if the pure binary held in memory is representing instructions or data simply by looking at it
• A CPUs performance is affected by: clock speed, cache size, number of cores, SSD, RAM, HDD
• Clock speed is the number of cycles per second, measured in Hertz (Hz)
• Cache size is temporary storage of data and instructions being read to and written it is faster to transfer to and from cache than transferring to and from RAM
• Number of cores is how many instructions can be processed at the same time, a core is a complete copy of the CPU
• Embedded systems is a computer system with a dedicated function within a larger mechanical system
• Properties of an embedded systems: small size, low power consumption and low cost per unit
• Types of busses: Address bus - carries addresses, Data Bus - carries data, Control Bus - carries control instructions
• Decode: Inspects the instruction and works out what it is that needs doing
• Fetch: fetching the next instruction from main memory and bringing the instruction back into the CPU
• Execute: carries out the instruction
• Fetch:

  Address from the PC is copied to the MAR

  Instruction from the MAR is fetched and copied to MDR

  The instruction copied is sent to the CIR

  Increment the PC
• Decode:

  The instruction in CIR is decoded by the control unit

  Data may be loaded into the MDR
• Execute:

  The instruction is performed

  The ALU may be used for any logic or calculations

  The result is stored in the accumulator