CompTIA A+® Certification All-In-One For Dummies®, 2nd Edition

4.1. Understanding System Resources

In this chapter, when you see the term system resource, think of it as a setting assigned to a device that allows it to function within the computer. A device is any piece of hardware that you can install on the computer: for example, a network card, modem, or sound card.

The three major system resources that can be assigned to devices are I/O addresses, IRQ addresses, and DMA addresses. A fourth system resource — a memory address — can sometimes be assigned to devices as well. In the following sections, I discuss each of these system resources.

4.1.1. I/O addresses

It is extremely important to remember that the CPU (processor) is the traffic cop of the entire system. If something is going to happen on the system, the CPU usually enables the action. All devices in the computer need to communicate with the processor from time to time, and the processor needs a method of separating and prioritizing all these communications.

Because the processor needs to send information to a number of different devices, and because those devices need to know which messages coming from the CPU are for them, each device is assigned an I/O (input/output) address. The I/O address is a special port address that represents a pathway between the CPU and the device. So, for example, if the processor needs to send information to LPT1, it can send the information to pathway 0378–037F, which is the pathway address that leads to LPT1. (For more on the standard I/O address ...