Computer system resources

Quick links

System resource ABCs
What is an IRQ?
What is an I/O?
What is a DMA?
Checking resource availability
Assigning a resource setting
Changing resources
All IRQs are used, now what?
Can I add an IRQ?
IRQs not recommended

System resources ABCs

System resources are what allocate and setup your hardware components, helping hardware to work without causing issues with other hardware within your computer. System resources are setup by one or more of the below.

What is an IRQ?

Short for Interrupt request, IRQ is a signal that has a direct line to the computer processor, allowing it to stop the processor momentarily and decide what to do next. Every IBM compatible computer has a maximum of 15 IRQs and are prioritized in the computer according to the importance of the device. See our IRQ definition for additional information, related links, and a listing of IRQs.

What is an I/O?

Input Output (I/O) represents the locations in memory that are designated by use of various devices to exchange information amongst themselves and the rest of the PC. See our I/O port definition for further information and related links.

What is a DMA?

DMA, or Direct Memory Access, are pathways provided by the hardware to allow the hardware direct access to the computer's memory. See our DMA definition for further information, related links, and a listing of DMAs.

Checking resource availability

If you have Windows 2000 or Windows XP, follow the steps below. Click Start, Programs, Accessories, System Tools, and then System Information to display the system resource information.

If you have Windows 95, Windows 98, or Windows ME, follow the steps below.

  1. Open Device Manager.
  2. Double-click on the computer (the first icon listed in Device Manager. This will list numbers 00 - 15; any number that is not listed is an indication that the IRQ is free. If all numbers are listed once or more, this would be an indication that all IRQs are being used.

In Windows 3.x or MS-DOS, to determine the currently used resource settings, use the MSD command, located in the DOS directory.

Assigning a resource setting

Many devices still in use today use Jumpers to setup the Resource settings for a hardware device. If your card has Jumpers it is recommended that you set the jumpers to available settings on your computer and then install the software on the computer to help resolve issues from occurring.

If your card has no jumpers or dip switches, it is a good possibility that the card is a Windows card (Plug N Play card). This indicates that you should be able to place the card within the computer and Windows 95 or Windows 98 will setup the card for you. Many of these cards are configured through the software used to install the card or Device Manager.

Changing resources

Within Windows 95 and Windows 98, most PnP (Plug N Play) cards can be manually adjusted through Device Manager. If your device is encountering conflicts with another device within Device Manager, double-click the device within the device category. Such as double-clicking a 3COM NIC icon under Network Adapters. Within the properties of the device click the Resource tab. In Resources uncheck the box that says 'Use automatic settings'; once unchecked you will then be able to change the Basic Configuration. As you change the Basic configuration, each of the resource settings will change. If you only have one option for resource settings, it's a good possibility that the device may be a Legacy device or may only work with one configuration mode.

All IRQs are used, now what?

If your computer is utilizing all IRQs, unfortunately there are only a few ways around this, which can be very complicated. The first and easiest way would be to attempt to remove devices from the computer to allow IRQs to become free or substitute for external devices. The other option would be to attempt to assign the IRQ settings to IRQ settings that may already be used by another device. However, when doing this, it is recommended that you choose a device that is not going to be frequently used. Windows may report that there is a device conflicting; however, in some instances the devices can work on the same IRQ the devices but will not be able to work at the same time.

Can I add an IRQ?

No, unfortunately with PCs they are limited to 00-15, even the latest PCs have this limitation. However, you can add devices such as a SCSI card to the computer, daisy chain a hard drive and CD-ROM drive and other hardware devices, and because the SCSI card uses ID addresses, when the hardware devices are hooked up to the SCSI card, they will not be taking an IRQ. Therefore, seven devices could be used on one IRQ. Another recommended connection to PC computers would be the USB port, which allows up to 127 devices to be connected at once using only one IRQ.

IRQs not recommended

When connecting devices it is recommended that you stay away from IRQ 9 which is a cascade port with IRQ 2. However, it is a good idea to assign devices that you want to move and do not plan to use to IRQ 9 to allow extra IRQs for a device you may plan to use. A good example of this recommendation is moving the MPU-401 device, which is a midi device used for musical keyboards.

Additional information

  • See our IRQ definition for further information and related links on this term.