2.9"Resources" for both Device and Driver

Thus device drivers must be "attached" in some way to the hardware they control. This is done by allocating bus-resources (I/O, Memory, IRQ's, DMA's) to both the physical device and letting the device driver to find out about it. For example, a serial port uses only 2 resources: an IRQ and an I/O address. Both of these values must be supplied to the device driver and the physical device.

The driver (and its device) is also given a name in the /dev directory (such as ttyS1). The address and IRQ number is stored by the physical device in configuration registers on its card (or in a chip on the motherboard). Old hardware (in the mid 1990's) used switches (or jumpers) to physically set the IRQ and address in the hardware. This setting remained fixed until someone remover the computer's cover and moved the jumpers.

But for the case of PnP (no jumpers), the configuration register data is usually lost when the PC is powered down (turned off) so that the bus-resource data must be supplied to each device anew each time the PC is powered on.

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