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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
IRQ listing
DMA channels
SYSTEM RESOURCE
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 IRQ Listing for a list of IRQs and which may be available or
are currently used.
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 IRQ Listing for a list of
IRQs and I/O ranges.
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 DMA Listing
for listing of DMA channels.
CHECKING RESOURCE AVAILABILITY
In Windows 3.x or
MS-DOS, to
determine the currently used resource settings, use the MSD
command,
located in the DOS directory.
If you have Windows 95,
Windows 98, or Windows
ME, follow the below steps.
- Open Device Manager.
- 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.
If you have Windows
2000 or Windows XP, follow the
below steps. Click Start, Programs, Accessories, System
Tools, and then System Information to display the system
resource information.
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 / 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 and/or Device Manager.
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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 which 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.
Step by step instructions for changing
the resources for a device under Windows 9x can be found at CH000197.
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 and 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. The latest and greatest PCs
will also have this limitation. However, you can add devices such as a
SCSI
card to the computer, daisy chain a hard drive / 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, you will be able to utilize
up to 7 devices 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, generally it is a good idea to assign devices that you
wish 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.
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