I for one would like to say a word of appreciation and thanks to the moderators who help so many people on this forum. I would also like to remind all you people who post your urgent problems on any of the forums that it only takes a minute to say "thank you" to the person who helps you resolve your problem. I know how very frustrating it is to follow a problem until it is (presumably) resolved and then have the person who posed the problem disappear without any acknowledgement of having been helped. Think how you would feel is you had invested your time and your expertise in helping someone and they didn't even say "thank you." - jayt 
Tutorials | What are IRQs
Publish date: 17:50 Thursday, 28th July 2005
Written by:
MishY
Audience intended for:
Windows ME Users, Windows 98 Users, Windows 95 Users
Category: Windows
What are IRQs ?
Interrupt Request Line Back in the days of Windows 3.1 the process of installing a new modem, network interface, or other card was very hit or miss. You plugged your card into the slot and waited to see if its IRQ would happily coexist with the ones for all the other hardware in your PC. If it didn't, readjusting the settings was a nightmare.
Nowadays, adding a new card is much easier thanks to Windows Plug&Play technology. However many of today's PC's are victims of their own success. Some come with so many internal devices (each preconfigured with it's own preset IRQ) that you may actually run out of free IRQs before you can install a new card or device. Much of today's PC hardware components communicate with you system through an IRQ. -
Whenever a device has a task for the CPU; it sends a signal to the CPU via an IRQ- When the CPU sees the signal, it interrupts its current task and gives it attention to the device. Before you buy a new card or device find out whether it needs an IRQ. Significant exceptions include most video cards, USB devices, and EIDE or SCSI drives like CD-ROM drives or hard disks. (The IRQ's that these devices use are automatically assigned to the USB, EIDE or SCSI bus rather than to the device itself). If you new hardware does need an IRQ, figure out how many IRQs your computer has. Unfortunately most systems come from the factory with only a few unused IRQs. A typical PC has a total of 16 IRQs, numbered 0 to 15.
To see how many IRQs are free on your PC go to : For Win 98 Start/Programs/Accessories/SystemTools/SystemInformation/click Hardware Resources/and then IRQs. For Win 95 highlight the MyComputer Icon and go to Properties/Device Manager/then double click on the Computer icon at the top of the list.
If you have one or more unused IRQs your PC and Windows should automatically assign your new hardware with a free IRQ during installation. But if all your IRQ's seem to be in use there are some ways round that .. *See "Freeing IRQ" article for more details*
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