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System Resources


A line of a motherboard bus that a hardware device can use to signal the CPU that the device needs attention. The hardware device places a voltage on the Interrupt Request (IRQ) line Some lines have a higher priority for attention than others.  Each IRQ line is assigned a number (0 to 15) to identify it.


I/O (port) addresses

Numbers assigned to a hardware device that software uses to send a command to a device.  Each device 'listens' for these numbers and responds to the ones assigned to it.  

I/O addresses are communicated on the address bus  

Memory addresses

Numbers assigned to physical memory located either in RAM or ROM chips.  Software can access this memory by using these addresses.  

Memory addresses are communicated on the address bus  


DMA - Direct Memory Access

A number designating a channel on which the device can pass data to memory without involving the CPU.


  The CPU is freed up by components using Direct Memory Access 

IRQ memory jogger 

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