The concept of memory locations expressed in hex is important in order to understand what comes next. Each device using resources in the system is assigned a logical, hexadecimal name by the BIOS. If you recall your trip into the Device Manager to review the resources used by a modem, you doubtless noticed that the resources were expressed in hex. These are the memory locations that the resources use and where they can be accessed.
The BIOS assigns Logical Names to the devices using an IRQ and memory address. Now IRQ 3 and I/O address 2F8-2FFh becomes Com 2.
This does not mean that you cannot change the standardized IRQ and I/O address. Be strongly cautioned however against doing this, "just because you can". Moreover, whenever you are building or working on a new system, be strongly advised to create a map of the system before you start making any changes.
Table 19 shows a listing of the typical assignments for IRQs and I/O addresses in a PC.
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