IRQ IO and DMA Addresses.txt

An IRQ allows a device to request certain system resources on priority. Normally, the system allowcates the different non-competing IRQ numbers to different devices. The system allocated IRQs may some times be manually changed. However, it may lead to serious IRQ conflicts resulting in a hung operating system.

System Timer

This IRQ is used within the system board for system timing.

Assigned to the Keyboard Controller

Tied to IRQs 8-15

COM 2

Assigned to the serial ports COM 2, and COM 4.

COM 1

Assigned to the serial ports COM 2, and COM 4.

LPT2 or Sound Card

Assigned to a secondary printer port LPT2. If LPT2 is not available, used for sound card.

Assigned to the Floppy Diskette Controller.

Assigned to the parallel port LPT1.

Reserved for the internal Real-Time Clock

Substitutes for IRQ 2

This IRQ uses IRQ 2 to talk to the CPU. Normally used for network cards.

Not Assigned

Can be used for network card, or others.

Not Assigned

Left open for use with any other device.

PS/2 Mouse Port

Used for the PS/2 style mouse port normally available on many motherboards.

NPU (Numerical Processing Unit)

Used for math co-processor.

Assigned to the Primary Hard Disk Controller

Assigned to the Secondary Hard Disk Controller

Input/output addresses ( I/O addresses for short) are resources used by almpst every device in the computer. The I/O addresses represent the location in memory for a given device to exchange information between itself, and the rest of the system. These address spaces are permanently allocated to the system devices. If an address space allocated to one device (say, LPT) is assigned to another device (say, IDE controller) than I/O address conflict will arise, and the system may hang or not function normally.

Used by keyboard controller

Used by SCSI host adapters

Secondary IDE Interface

Primary IDE Interface

Default address for Sound cards

Optional address for sound cards and network cards

Optional address for sound cards and network cards.

Assigned to LPT2 or LPT3

Optional address for sound cards and network cards

Default for many network cards

Assigned to COM 4 and used with IRQ 3

Assigned to COM 2 and used with IRQ 3

Other Network Interface Card choice

Used for a SCSI host adapter or MIDI device. You can use this for a Network card when not assigned to any SCSI or MIDI device.

Used for the SCSI host adapters

Could be used for a SCSI host adapter

Could be used for a Network card, provided there are no conflicks.

This is assigned to the first parallel printer port (LPT 1) in color systems. Normally used with IRQ 7.

This is assigned to the first parallel printer port (LPT1) in monochrome systems.

Assigned to COM 3 and used with IRQ 4

Assigned to COM 1 and used with IRQ 4

A technique for transferring data from main memory to a device without passing it through the CPU. Computers that have DMA channels can transfer data to and from devices much more quickly than computers without a DMA channel can. This is useful for making quick backups and for real-time applications.

Channel Number: The number of the DMA channel from 0 to 7.Bus

• Line: Indicates whether or not this DMA channel is available to expansion devices on the system bus. This will say "8/16 bit" for DMA accessible by all expansion devices, "16 bit only" for a channel available only to 16-bit cards, or "No" for a channel
• reserved for use only by system devices.

Typical Default Use: Description of the device or function that normally uses this DMA channel in a regular modern PC.

• Other Common Uses: This is a list of other devices that commonly either use this channel or offer the use of this channel as one of their options. This list isn't exhaustive because there are a lot of oddball cards
• out there that may use unusual DMAs.

Description: A description of the channel and how it is used, along with any relevant or interesting points about it or its history.

Conflicts: A discussion of the likelihood of conflicts with this DMA channel and what are the likely causes.

Channel Number: 0

Bus Line: No

Typical Default Use: Memory (DRAM) Refresh.

Other Common Uses: None; for system use only.

• Description: This DMA channel is reserved for use by the internal DRAM refresh circuitry. Dynamic RAM (used for system memory on almost all PCs) must be refreshed frequently to make sure that it does
• not loseits contents. DMA channel 0 is used for this purpose and is not available for use by peripherals.

Conflicts: Most devices stay far away from DMA0, recognizing its use by the system. Beware however, as some devices actuallyoffer DMA0 as an option. For example, some sound cards do. Do not useDMA0 for peripherals. If you have no devices set to use DMA0 but a conflictbecomes apparent anyway, it could be a problem with your motherboard.

Channel Number: 1

Bus Line: 8/16-bit

Typical Default Use: Low DMA channel for sound card.

Other Common Uses: SCSI host adapters, ECP parallel ports, tape accelerator cards, network cards, voice modems.

• Description: This DMA channel is normally taken by
• the sound card in your PC for its "low" DMA channel. Most sound cards today actually use two DMA channels; one must be chosen from DMAs 1, 2 or 3,
• while the other can be any free DMA channel (and so is selected from the less-used 5, 6 or 7). DMA1 is also a popular choice for many other peripherals,
• largely for historical reasons (on the original XT, DMA3 was used for the hard disk so DMA1 was all that was left open for everything else to share).

• Conflicts: DMA1 is one of the two most contested
• channels in the system (the other being DMA3, which is often worse). It is important to watch for conflicts between multiple devices here, particularly if
• you are using a sound card. It is preferable in general to leave the sound card on DMA1 and move any other devices out of its way, for compatibility with older (poorly written) software that assumes the sound card is on DMA1. Also watch out for ECP parallel port conflicts here. More general solutions to resource
• conflicts can be found in the conflict resolution area of the Troubleshooting Expert.

Channel Number: 2

Bus Line: 8/16-bit

Typical Default Use: Floppy disk controller.

Other Common Uses: Tape accelerator cards.

• Description: This DMA channel is used on virtually
• every PC for the floppy disk controller. As such, it is usually not offered as
• an option for use by most peripherals. Some do offer it as an option however. In particular, tape accelerator cards often offer the use of DMA2 as an option. This is probably because these cards are used for tape drives that run off the floppy interface, and many of them can be set to drive floppy disks themselves.

• Conflicts: DMA2 is not often a source of conflicts,
• as long as you remember not to put any other devices on it if you have a floppy disk controller in your system (which almost everyone does). Beware tape
• accelerator cards that default to DMA2 for their channel assignment.

Channel Number: 3

Bus Line: 8/16-bit

Typical Default Use: None.

Other Common Uses: ECP parallel ports, SCSI host adapters, tape accelerator cards, sound card (low DMA), network cards, voice modems.

• Description: This DMA channel is normally the only
• one free on the first controller (DMAs 0 to 3) when you are using a sound card. As a result, it is probably the "busiest" channel in the PC, with many different devices vying for its services. One of the most common uses of this channel is by ECP parallel ports, which require a DMA channel unlike other parallel port modes. On very old XT systems, DMA channel 3 is used by the hard disk drive.

• Conflicts: DMA3 is probably the worst channel in the
• system for conflicts, because so many devices try to use it. It is important to watch for conflicts between multiple devices here, particularly if you are using a sound card or ECP parallel port.

Channel Number: 4

Bus Line: No

Typical Default Use: Cascade for DMA channels 5 to 7.

Other Common Uses: None; for system use only.

• Description: This DMA channel is reserved for
• cascading the two DMA controllers on systems with a 16-bit ISA bus. It is not available for use by peripherals.

• Conflicts: There should not be any conflicts on this
• channel; any problems with it indicate a possible system hardware failure.

Channel Number: 5

Bus Line: 16-bit only

Typical Default Use: High DMA channel for sound card.

Other Common Uses: SCSI host adapters, network cards.

• Description: This DMA channel is normally taken by
• the sound card in your PC for its "high" DMA channel. Most sound cards today actually use two DMA channels; one must be chosen from DMAs 1, 2 or
• 3 (the "low" channel), while the other is selected from a high-numbered channel like this one. Some network cards also use this channel, though others don't use DMA at all.

• Conflicts: Few conflicts arise with this channel
• because there are relatively few devices that can use DMA channels 5, 6 or 7.

Channel Number: 6

Bus Line: 16-bit only

Typical Default Use: None.

Other Common Uses: Sound cards (high DMA), network cards.

• Description: This DMA channel is normally open and
• available for use by peripherals. It is one of the least used channels in the system and is an alternative location for the "high" sound card DMA
• channel or other devices.

• Conflicts: Few conflicts arise with this channel
• because there are relatively few devices that can use DMA channels 5, 6 or 7.

Channel Number: 7

Bus Line: 16-bit only

Typical Default Use: None.

Other Common Uses: Sound cards (high DMA), network cards.

• Description: This DMA channel is normally open and
• available for use by peripherals. It is one of the least used channels in the system and is an alternative location for the "high" sound card DMA
• channel or other devices.

• Conflicts: Few conflicts arise with this channel
• because there are relatively few devices that can use DMA channels 5, 6 or 7.