1.1 System Architecture V2

1.1 System Architecture V2

1. System Buses

   • Used to reduce the amount of data collisions
   • Data Bus - Carries instructions from the main memory to the processor
   • Address Bus - Carries addresses from processor to main memory, it is unidirectional
   • Control Bus - Instructs which data will be travelling to and from memory

2. Internal Components - The Processor, Main Memory (RAM, ROM, EEPROM), I/O Controllers, Buses

3. External Components - Keyboard, mouse, printer, disk drives, I/O Devices/ I/O Ports, Secondary Storage (External Hard drive)

4. ROM - Read Only Memory

   • Bootstrap ladder is held in ROM, gives the instruction to start up the Operating System

5. I/O Controllers - These are used to allow an interface between a hardware device external to the motherboard and the processor.

   • I/O Controllers are used for: Keyboard, Mouse, Disk Drive

6. More Cores = More instructions can be processed simultaneously

7. Embedded Systems

   • Hertz - Number Of Cycles Per Second
     • Processor Speed - Measured In Hertz
     • Typical speeds have spanned across MHz and GHz
   • A system within another device e.g. central heating system, dishwashers, fridges, washing machines

8. The purpose of the CPU is to carry out program instructions.

   • Each CPU is designed to execute a specific group of instructions. The CPU carries out a series of functions in a continuous cycle

9. CPU automatically checks cache for instructions before it requests data from RAM. This saves fetching the instructions and data repeatedly from RAM – a relatively slow process.

10. Cache - Small amount of memory that is a part of the CPU - closer to the CPU than RAM. Used to temporarily hold instructions and data that the CPU is likely to reuse

11. Motherboard - A circuit board that connects the CPU to the memory The CPU sits on the motherboard (also called the logic board).

12. Buses - Circuits on the motherboard which connect the CPU to other components..

    • A bus moves instructions and data around the system
    • The speed of a bus is measured in megahertz (MHz). The faster the bus, the faster data is communicated. The speed of the motherboard is defined by the bus speed.

13. Bridges - Manage how data + instructions are transferred CPU, memory and other devices.

14. ROM (read only memory) is non-volatile Non-volatile means that its contents cannot be changed and it retains its memory after the computer is turned off.

15. Rom contains BIOS which is the firmware to the motherboard. The BIOS contains the bootstrap

    • It happens between turning on the power and the computer beeping to say it is starting to load the OS. This process is known as POST (power on self test) on a PC.
      • The boot sequence is the computer's initial start-up process. After the boot, the OS controls the CPU and supplies the programs to run.

16. PROM - Made as blank ROM. PROM chips can be bought cheaply and programmed directly by a programmer. They are not rewritable so they can only be programmed once.

17. EEPROM (electrically erasable programmable read-only memory) - firmware can be easily updated, similar to a rewriteable CD