1.1 System architecture

Computers receive a binary sequence from an input device and have to use their Instruction set to decode what it means.

If the sequence does not match an instruction there is an error

If the sequence matches something in the instruction set the instruction is carried out

Embedded system

  • An embedded system is one which has a processor built in to another device

  • Usually for very specialised tasks

  • Doesn’t contain an operating system

  • Dishwasher, Microwave, Fridge, Smartphone, TV

CPU performance

The purpose of the CPU is to carry out the processing of data on the computer system

The CPU fetches, decodes and executes instructions

  • Clock speed

    • This determines the rate at which instructions are carried out

    • The clock speed is measured in Hertz(Hz)

    • 1Hz is 1 cycle per second

    • Average Hz is 60Hz

    • A 3.6Ghz processor carries out 3.6 billion calculations a second

  • Cache Size

    • Cache memory is a buffer that sits between the CPU and main memory

    • The larger the cache the more space there is for instructions

    • The cache has a similar access speeds to the CPU and is therefore quicker to fetch instructions

  • Number of Cores

    • A core is an independent processor in the CPU

    • A dual core has 2, Quad 4, Hex 6

    • The higher the number of cores the more instructions that can be executed simultaneously

Von Neumann architecture

The Von Neumann architecture describes a system where data and programs/instructions are stored in the same memory location

The FDE cycles is the process of fetching these instructions from memory and executing them

  • PC-program counter

    • Points to next instruction

  • MAR-Memory address register

    • Stores the address of instruction or data

  • MDR-Memory data register

    • Stores actual instruction or data

  • CIR-Current instruction register

    • Holds the current instruction to be executed

  • ALU-Arithmetic logic unit

    • Temporarily stores arithmetic and logic results

FDE

  • Fetch

    • Address from the PC is copied to the MAR

    • Instruction from the MAR is fetched and copied to the MDR

    • The instruction in the MDR is copied to the CIR

    • Increment the PC

  • Decode

    • The instruction in the CIR is decoded by the Control Unit

    • Data may be loaded into the MDR

    • Instruction set is used to check the instruction

  • Execute

    • The instruction is performed

    • The ALU may be used for any logic or calculations

    • The result is stored in the accumulator