Operating system & Architecture Flashcards
Operating Systems
Loads software Manages hardware Manages error handling Manages user accounts Allows multitasking Provides an interface
Interrupt
A signal sent to the processor
Requests processor time
Processor stops to service interrupt
Interrupts have different priorities
Control bus
Carries signals
Directs the CPU
Can be unidirectional or bidirectional
Data bus
Carries data that is being processed
Data travels in both directions (bi-directional)
Address bus
Carries address locations of next item to be fetched
Data travels one way ( unidirectional)
Registers
PC- Program Counter MAR- Memory address register MDR- Memory data register CIR- Current instruction register ACC- Accumilator
Control Unit
Controls operation of memory, processor and input/output
Fetches each instruction in turn
Interprets instructions
Sends signals to other components telling them what to do
ALU (Arithmetic Logic Unit)
Carries out calculations
Carries out logic operations
Holds values during calculations in a register called an accumulator (ACC)
Stored program concept
Programs / instructions are stored in memory
Data is stored in memory
Instructions are fetched and executed one after another
Fetch Execute Cycle 1
Program counter(PC) has address of next instruction to fetch
Fetch Execute Cycle 2
Address in program counter copied to memory address register (MAR) via address bus
Fetch Execute Cycle 3
Instruction copied from memory to memory data register(MDR)
Fetch Execute Cycle 4
Instruction copied from MDR to the current instruction register (CIR)
Fetch Execute Cycle 5
Value in PC incremented to point at next instruction to fetch
Fetch Execute Cyle 6
Address of instruction placed in MAR
