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• ULTRA DMA/33
• MAINBOARD FORM FACTORS
• IRQ TABLE
• SB-LINK
• MULTIPLIER DIGITAL CODE

IRQ Table

The following IRQ allocation table could provide some help if you are experiencing problems adding new devices to your system that need an IRQ. Don`t forget to check out the remarks on the bottom of this page for more useful tips on this matter.

Remarks:

1. As you can see in the above overview, in a fully `enabled` system, only three (3) IRQ`s are available for your add-on card

2. Many PCI VGA cards do not need an IRQ. If this is the case with your VGA card, then you can disable the `Assign IRQ to VGA` setting in the `Integrated Peripherals` section of the BIOS.

3. Some PCI cards, such as the Adaptec AHA-3940 dual channel Ultra Wide SCSI adapter, will need 2 IRQ`s. When inserting this card into a PCI slot, make sure the next PCI slot has no cards in it as that slot`s IRQ will already have been taken by the AHA-3940.

4. Even though the USB can be disabled in the BIOS setup (`Assign IRQ to USB`), it will still show up in the Device Manager of Windows 95 (OSR2). This will not influence your system`s behavior or performance, however.

SB-Link

SB-Link is a connector on the mainboard (for example 6LTM2) which is especially for use with a Creative Labs PCI soundcard. The SB-link guides signals from the ISA bus to the PCI soundcard through a cable which comes with the PCI soundcard. This is necessary because some DOS based games address the ISA bus directly. In this way compatibility with these games is guaranteed. The official explanation of SB-Link (as posted on Creative Labs website) is as follows:

SB-LINK combines Intel's PC-PCI and "Serialized IRQ" protocols. These technologies can be found in Intel's TX, LX and newer core logic chip sets. This technology provides the DMA and IRQ signals present in ISA Bus today, but not available on the PCI Bus. The SB-LINK serves as a bridge between the motherboard and PCI sound card to deliver Sound Blaster 16 compatibility for real-mode DOS games, a widely accepted audio standard in Multimedia Personal Computers. SB-LINK, endorsed by leading motherboard suppliers, is becoming a standard audio connector on new motherboards. With SB-LINK, sound card users can look forward to the best gaming experience ever.

Multiplier Digital Code

Multipliers are digital codes which are presented to the CPU and which define the number of times the CPU busfrequency will be multiplied inside the processor.

On early 586 mainboards this digital code was defined with two pins (BF0, BF1).

With two pins 4 different combinations were defined:

When Intel wanted to release its 233MHz MMX CPU, the then latest mainboards (HX chipset based) still used only these two pins for the multiplier selection. That's why they decided that they would start over and use the 0 0 code, which was used for the 1.5 multiplier, also for 3.5.

Because AMD wanted to make Socket 7 CPUs with even higher speeds, there was a necessity to add another multiplier pin to extend the multiplier selection possibilities, BF2. Now the following 8 combinations were possible :

Note: Intel nowadays often fixes the multipliers of its CPUs to a certain value in order to limit the overclocking possibilities of its processors. In this case, no matter what code the mainboard offers to the CPU, it will always use the same value.

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