(IRQ, DMA and I/O ADDRESSES)
resources are what allocate and setup your hardware components helping
preventing hardware to work without causing issues with other hardware
within your computer. System resources are setup by one or more of
Interrupt Request (IRQ)
Direct memory access (DMA)
find out about system resources in Windows vista/7 follow these steps:
Click My Computer and go Manage
WHAT IS A IRQ?
An IRQ or Interrupt request line allows a hardware device inside of
the computer a direct line to the Microprocessor and tells the Microprocessor
to stop what it is doing and wait until it has further instructions.
Every PC computer has a maximum of 16 IRQs and is prioritized in the
computer according to the importance of the device.
Here is the IRQ Listing
IRQ Channel Assignment
0 System Timer
2 Cascading with 9
3 COM 2 or COM 4 (Serial or IRDA devices)
4 COM 1 or COM 3 (Serial or IRDA devices)
5 LPT2 or Sound Card
6 Floppy Drive Controller
7 LPT1 (Parallel Devices)
8 Real Time Clock
9 Cascading with 2
12 PS/2 Mouse Connector
13 Math Co-processor
14 Primary Hard Drive Controller
15 Secondary Hard Drive Controller
is an example of the IRQ Properties found on a typical computer
WHAT IS A DMA?
A DMA or Direct Memory Access is a pathway provided by the hardware
to allow the hardware direct access to the computers memory. This
feature allows devices to bypass the CPU and write their information
directly to the main memory.
DMA Channel Assignment
1 Sound Card
2 Floppy Drive Controller
3 Open (ECP or parallel port)
4 2nd DMA Controller
WHAT IS A I/O?
An Input Output (I/O) represents the location in memory that is designated
by use of various devices to exchange information amongst themselves
and the rest of the PC.
Device I/O Address Range
System Timer 040-043
COM 1 3F8-3FF
COM 2 2F8-2FF
COM 3 3E8-3EF
COM 4 2E8-2EF
Floppy Drive Controller 3F0-3F7
Sound Card 220-xxx
IDE Primary 1F0-1F7
IDE Secondary 170-177
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
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.
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.
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 however will not be able to work at the same
CAN I ADD AN IRQ?
No, unfortunately with PC's they are limited to 00-15. The latest
and greatest PC's 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.