Topic 3: Computers Flashcards
Von Neumann architecture
A structure in which the hardware is connected and organised.
It consists of Main Memory and a Central Processing Unit interconnected by buses.
__________Main Memory
________ (Read)!_____¡(Write)
Input –> Central Processing Unit –> Output
The CPU reads and writes data & program instructions to and from main memory.
Main memory
Known as Random Access Memory(RAM)
It stores the data & programs the CPU can access.
Volatile - Loses content when power is lost.
Faster and more expensive than secondary storage
Programmable computer
A computer that is multi-purpose, can be programmed to carry out different tasks. They are able to store program instructions and data in main memory.
CPU parts
Consists of:
- Control Unit (CU)
- Arithmetic Logic Unit (ALU)
- Registers
Control Unit (CU)
Decodes instructions received from main memory and coordinates the actions of the other parts of the CPU.
Arithmetic Logic Unit(ALU)
Performs arithmetic and logic operations on data.
Registers
Provides fast, temporary storage for instructions.
Buses
Buses connect the components inside a computer.
Types:
- Address bus
- Data bus
- Control bus
Adress bus
Carries the address of the memory location. Unidirectional, only the CPU can put an address on this bus.
Data bus
Holds the value being read from or written to memory. Bidirectional.
Control Bus
Carries command signal from the control unit to other components. The status signal is sent back to the CPU. Bidirectional.
Clock
A tiny quarts crystal that vibrates and sends out electronic signals to synchronise the actions of the hardware components.
Measured in hertz, 1 hertz = 1 “tick” per second.
Fetch/Decode/Execute cycle
Program instructions and data are stored in main memory and transferred/fetched one data at a time to the CPU, where they are decoded and executed.
Fetch: The control unit sends a read signal to main memory along the control bus. It also places the memroy address of the next instruction on the address bus. The RAM copies the content of the memory location indicated by the address bus on the the data bus.
Decode: The control unit decodes the instructions.
Execute: The control unit sends signal to the other components of the CPU instructing them what to do.
Secondary storage
Non-volatile
Allows the system to store data and programs permanently.
Cheaper and slower than main memory.
Types:
- SSD(Solid State Drives): USB drive
- Magnetic storage: HDD(Hard Disc Drive)
- Optical Storage: DVD/CD
Magnetic storage
A head reads & writes to spinning discs.
An area that is magnetised represents a 1.
An area that is not magnetised represents a 0.
