Systems Architecture

Systems Architecture

1. Computer Systems

   • Hardware = The physical parts in a computer system e.g. CPU, Keyboard
   • Software
     • The programs that a computer system runs e.g. OS, Games, Browser
   • Embedded Systems
     • Computers built into other devices usually as control systems e.g. Dishwashers, Microwaves, SatNavs
     • Easier to design, cheaper to produce and more efficient

2. CPU

   • Components
     • CU = Control Unit = Controls the flow of data in and out the CPU and manages the fetch decode execute cycle
     • ALU = Arithmetic Logic Unit = Does calculations such as addition, multiplication, etc as well as binary shifts and logic operations
     • Cache = stores regularly used data for quick access
       • +Speed = -Capacity
       • +Capacity = - Speed
     • Registers = Temporarily holds small amounts of data. Extremely Fast
   • Factors affecting performance
     • Number of Cores
       • Each core processes data independently so more instructions can be carried out per second if the number of cores is increased
     • Clock Speed
       • Number of instructions a single processor can carry out in a second
       • Cache Size = larger the cache gives the CPU access to more faster data

3. Von Neumann Architecure

   • Data and instructions are stored in the same place in memory
   • PC = Program Counter = Holds the memory address of the next instruction for each cycle
   • Accumulator
     • Stores results of ALU calculations
   • MAR = Memory Address Register = Holds any memory address about to be used by the CPU
   • MDR= Memory Data Register = Holds the actual data or instruction either fetched from memory or waiting to be written

4. Fetch-Execute Cycle

   • Memory address copied from PC to MAR instruction copied from memory to MDR PC incremented by 1
     • Fetch
   • Decode
     • Instruction in the MDR decoded by the CU CU prepares for next step e.g. loading values into the MAR or MDR
   • Execute
     • Instruction carried out e.g. Load data from memory Write data to memory . Do calculation in ALU