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How Your Motherboard Affects Your Graphics Upgrade Options

Before you can get anywhere with a video upgrade, you need a place into which to install that upgrade. Based on the results of your "grand tour" investigation, you should now know where your current video is located. There are three major possibilities you might encounter, in order from best to worst:

  • You have an AGP graphics card—You can remove the old card and insert a better card.

  • You have motherboard-integrated video with an open AGP expansion slot on your motherboard—You can disable the on-board video and add a card.

  • You have a motherboard-integrated video without an AGP expansion slot—You can install a slow PCI video card, or opt for a motherboard upgrade that offers an AGP slot.

Figure 13.1 compares the rear of a system containing a graphics card with a system containing motherboard-integrated (built-in) video.

Figure 13.1Figure 13.1 Rear view of a micro-ATX system with motherboard-integrated video (top) compared to an ATX system with a slot-mounted graphics card (bottom).

Although some micro-ATX systems feature both built-in video and an AGP slot, many do not. Most full-size ATX systems have AGP slots. Fortunately, if you're upgrading a recent system with a separate graphics card, you can remove the old card and plug in the new card. However, not all slots are alike when it comes to video.

AGP Versus PCI Slots

The two major standards for slots suitable for video cards are as follows:

  • AGP

  • PCI

Figure 13.2 demonstrates where an AGP 4x graphics card and a PCI graphics card can be installed on a typical system.

Figure 13.2Figure 13.2 An AGP 4x graphics card (top left) can be installed only into an AGP slot (middle right), but a PCI graphics card (bottom left) can be installed into any open PCI slot (bottom right).

PCI slots have been around for over a decade, and their once-speedy 132MB/sec throughput for the 33MHz, 32-bit version used on desktop motherboards has been outstripped by the performance of AGP. See Table 13.1.

Table 13.1 AGP Standards

AGP Speed


Difference Compared to PCI

AGP Version




2x PCI





4x PCI


3.3V and 1.5V



8x PCI





16x PCI




*Not supported by current motherboard/graphics card designs.

^AGP 4x cards can run in AGP 2x mode if 4x is not supported by the motherboard.

#AGP 8x cards can run in AGP 4x mode if 8x is not supported by the motherboard.

Besides faster throughput, AGP has two other big advantages over PCI for video:

  • AGP has a dedicated direct connection to the processor instead of sharing bandwidth with other PCI slot and motherboard devices.

  • AGP can use onboard or motherboard RAM for handling 3D textures.

The advantages of AGP should make it obvious that PCI is obsolete for graphics card use. An open PCI slot should not be used for graphics unless your motherboard doesn't offer an AGP slot or if you prefer to implement a multiple monitor solution by installing two separate video cards. Although you can still buy PCI graphics cards, most mid-range and faster graphics chipsets no longer support the PCI slot, thus limiting your options.

Mark's Tip Sheet: Stuck with PCI? Get a Motherboard Upgrade and Move to AGP!

A few years ago when AGP was new, there wasn't always a big difference between the performance of early AGP cards and PCI cards. Now, the difference is huge and will only be more pronounced as chipset makers continue to abandon PCI. If your motherboard doesn't have an AGP slot, considering squeezing a new motherboard with an AGP 4x or faster slot into your upgrade plans. Keep in mind that you can buy a motherboard with both an AGP 4x or 8x slot and built-in video if you want to save some dough now and still keep your options open.

AGP Slots and Voltage Standards

If your motherboard has an AGP slot, you can choose from a wide variety of features and chipsets on many different graphics cards. However, you need to understand that not all AGP slots and cards can be interchanged with each other. As Table 13.1 indicates, different AGP standards support different voltages. For this reason, the appearance of AGP slots has changed over time.

Figure 13.3 compares three different types of AGP slots with each other and with PCI slots.

Figure 13.3Figure 13.3 An AGP 1x/2x slot (top) for legacy 3.3V cards compared with an AGP 4x slot for 1.5V cards (middle) and an AGP Universal/Pro slot (bottom). Note the keying is reversed on the AGP 1x/2x and AGP 4x slots to prevent inserting cards with the wrong voltage.

The AGP Universal/Pro slot shown in Figure 13.3 has a longer connector than either the AGP 1x/2x or AGP 4x slots. It is called a Universal slot because it isn't keyed; thus, it can accept both 3.3V and 1.5V cards. The additional length of the connector supports AGP Pro cards used in technical workstations. Because the AGP Pro section of the slot could damage non-Pro cards inserted into it, most motherboards that are equipped with a Universal/Pro slot block the Pro extension to prevent accidental insertion of non-Pro cards, as shown here.

Although most current AGP 4x and faster cards use a three-part connector (refer back to Figure 13.2) to support both legacy and current AGP slots, AGP cards with a two-part connector can be plugged into their native slot type or the AGP Pro/Universal slot only. If you are trying to install an older AGP card into a newer system, keep slot compatibility in mind.

ON the web: Eliminating AGP Slot Confusion the ATI Way

ATI Technologies offers a terrific visual tutorial to the many slot and connector flavors used by AGP. See it at the "ATI AGP Graphics Card Implementation" page at

AGP Is Not AGP—Details to Follow...

You won't see a headline like this in your local newspaper, but it's news to many PC users anyway—especially if your brand-new AGP card stubbornly refuses to work with your motherboard's AGP slot. Once again, a so-called standard proves to be anything but an airtight, "everything works with everything else" feature. How can you avoid getting burned when you try to match a new AGP video card with your AGP motherboard?

  • Check the electrical requirements of the card versus what the motherboard provides to the AGP slot. Some of the newest motherboards, such as Pentium 4 motherboards based on Intel chipsets, require 1.5V AGP 4x/8x video cards.

  • Make sure the slot supports the card speed you want to install.

Before you buy an AGP card for your system, or buy a new motherboard to work with your existing AGP card, check both vendors' web sites and third-party forums for compatibility issues. Also, make sure you install the latest motherboard chipset-specific drivers and card-specific drivers for best results.

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