Systems Architecture

Systems Architecture

1. Computer systems

   • a computer is a machine that processes data
     • purpose: take data, process it and output it
       • can be general purpose or dedicated systems
         • embedded systems: computers built into other devices, like a dishwasher or washing machine. dedicated to a single task,
     • consists of hardware and software.
       • hardware: physical stuff that makes up the computer system, eg. CPU, motherboard
       • software- the programs or applications that a computer system runs, eg. video game, operating system
     • contains components that work together, eg. CPU, power supply, heat sink, cooling fan, graphics card, motherboard, optical drive, RAM sticks, hard disk drive

2. CPU,: the brain of the computer. processes data and instructions to make the system work

   • 3 Main parts:
     • CU: Control Unit. overall control of the CPU. excecutes instructions with the FDE cycle. controls flow of data in and out of the CPU
       • • The program counter (PC) holds the memory address of the instruction for each cycle.
     • ALU: Arithmetic Logic Unit. does all the calculations and logic operations. contains accumulator register.
       • Accumulator- stores intermediate results of calculations in the ALU.
     • Cache: very fast memory in the CPU. stores regularly used data so that the CPU can access it quickly the next time it is needed.
       • MAR- memory address register - holds any memory address that is about to be used by the CPU. It might point to data or a CPU instruction.
       • MDR- memory data register- hold the actual data or instruction. This may have been fetched from memory, or waiting to be written to memory.
   • Follow the FDE cycle
     • Fetch Instruction: The memory address is copied from the PC to the MAR. The instruction stored in the MAR address is copied to the MDR . The PC is incremented to point to the address of the next instruction, ready for the next cycle.
     • Decode :The instruction in the MDR is decoded by the CU. The CU may then prepare for the next step, by loading values into the MAR or MDR.
     • Execute: The instruction is performed. This could be to: Load data from memory / Write data to memory / Do a calculation or a logic operation (using the ALU) / Change the address in the PC Or halt the program