Computer Systems

Computer Systems

• Internal components
• The processor
• The main memory (RAM, ROM , EEPROM)
• I/O controllers
• Buses
• External components (peripherals)
• Keyboard, mouse, printer, disk drives
• I/O devices / I/O ports
• Secondary storage

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• RAM - Random Access Memory
• Holds data and instructions that are currently in use by the processor
• Located on the motherboard
• Directly accessible by the processor
• All data/instructions are lost once power is turned off
• EEPROM - Electronically Erasable Programmable Read Only Memory
• E.g. Sim card / Flash memory
• Instructions/data can be erased electronically replaced

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• I/O Controllers
• These are used to allow an interface between a hardware device external to a motherboard (e.g. a keyboard) and the processor itself.
• I/O controllers are used for:
• Keyboard, mouse, disk drive, VDU
• System Busses
• A bus is a set of parallel wires connecting two or more independent components of a computer system in order to pass signals between them
• The system is split into three separate busses:
• Th data bus
• The address bus
• The control bus

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• The address bus
• Carries addresses from the processor to main memory or other I/O devices
• It is one direction (Uni-Directional)
• The processor generates an address
• All data/instructions are returned on the data bus
• The data bus
• Carries data/instructions from main memory to the processor (or from other secondary storage devices) to the processor
• Bi-Directional (two way)
• Data can be read/written

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• Control Bus
• Control signals are sent along the control bus
• E.g. memory read, memory write
• This instructs which data will be traveling to/from the memory
• Peripherals
• Peripherals are any devices that are not directly connected to the CPU
• E.g. mouse, keyboard, printer,hard disk drive, cd-rom drive
• These devices are also known as I/O devices (Input/Output Devices)
• I/O Ports
• I/O Ports allow communication from an I/O device and the motherboard (hence CPU)

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• Secondary Storage
• Used for long term storage of data and instructions
• Hard Disk Drive
• Solid State Drive
• Flash Memory
• DVD-R
• Blu-ray

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• Control Unit
• Sends Control Signals between the different internal components
• Memory Read
• Memory Write
• Hard Disk Drive Read
• I/O Write