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[ The PC Guide | System Optimization and Enhancement Guide | System Optimizations and Enhancements | System Resource (IRQ, DMA, I/O, COM) Conservation and Optimization ]

Free Up an ISA/VLB/PCI Expansion Card Slot

Many modern PCs have relatively few expansion slots; some have as few as three. Many of the smaller boxes that have few slots do not need as many in the first place because they have built-in components such as video cards; even still, expansion and adding peripherals can be difficult when there are few slots in the system. Even PCs with a number of slots can run out when you start adding a number of devices. Furthermore, modern PCs typically have a limited number of PCI and ISA slots, and depending on how you use your system, you may find that you have plenty of one type but not nearly enough of the other.

Here are a few ideas for freeing up an expansion slot, if this is an issue for you:

  • Free Up Slots Blocked by Port Connectors: Many PCs run out of expansion slots for a silly reason: the slots are being wasted because they are blocked by the connectors for the serial and parallel ports. While ATX form factor motherboards have these ports built into the motherboard itself, the conventional AT or baby-AT style motherboard uses ports that connect to the motherboard with a ribbon cable. These come with the motherboard installed into a piece of metal that fits into an expansion slot, to make assembling the PC faster (and cheaper). However, most modern cases have punch-out holes in the back of the case itself for these connectors. By unscrewing the connectors from the slot insert and screwing them into the holes in the back of the case, you can remove the inserts and free up a potentially wasted expansion slot--sometimes even two.
  • Remove Unnecessary Devices: You'd be surprised how often I find devices in PCs that were installed a long time ago but are no longer being used. Removing these unneeded cards will of course free up the slots they are using, if this is an option for you.
  • Make Optimal Use of VESA Local Bus (VLB) Slots: VLB slots are physically an extension of the ISA slot; the VLB slot is an ISA slot with two extra connectors on the end. ISA slots will therefore work in a VLB slot; if your ISA slots are all filled and there is a VLB slot free, you can use it. However, there are usually very few VLB slots on a VLB motherboard, so only put ISA cards there if you are out of ISA slots.
  • Optimize Shared Slots: Many PCI motherboards have a "shared" PCI/ISA slot. This is a slot that can either hold an ISA or a PCI card, but not both. It is possible because of how PCI cards are mounted "upside-down" to their slot inserts compared to how ISA cards are. If you have a board like this and you are out of ISA slots but have a free PCI slot, see if you have a PCI device in the shared slot, and if so, move it to the free PCI slot. Similarly if you are out of PCI slots but have a free ISA slot and an ISA card in the shared position.

Tip: IRQ conflicts can sometimes result from changing the slot a PCI card uses, due to how these devices are assigned IRQs.

Next: Free Up an IRQ by Combining IDE channels and Disabling Unused Ones

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