CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [118]
Figure 8-8 PCI expansion bus slots
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NOTE Before PCI, it was rare to see more than one type of expansion slot on a motherboard. Today this is not only common—it’s expected!
PCI Bus
32 bits wide
33-MHz speed
Self-configuring
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TIP There was a 64-bit version of the original PCI standard, but it was quite rare.
The original PCI expansion bus has soldiered on in PCs for over ten years. Recently, more advanced forms have begun to appear. Although these new PCI expansion buses are faster than the original PCI, they’re only improvements to PCI, not entirely new expansion buses. The original PCI might be fading away, but PCI in its many new forms is still “King of the Motherboard.”
AGP
One of the big reasons for ISA’s demise was video cards. When video started going graphical with the introduction of Windows, ISA buses were too slow and graphics looked terrible. PCI certainly improved graphics when it came out, but Intel was thinking ahead. Shortly after Intel invented PCI, they presented a specialized, video-only version of PCI called the accelerated graphics port (AGP). An AGP slot is a PCI slot, but one with a direct connection to the Northbridge. AGP slots are only for video cards—don’t try to snap a sound card or modem into one. You’ll learn much more about this fascinating technology in Chapter 19, “Video.” Figure 8-9 shows a typical AGP slot.
Figure 8-9 AGP slot
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NOTE The AGP slot is almost universally brown in color, making it easy to spot.
PCI-X
PCI Extended (PCI-X), available in such systems as the Macintosh G5, is a huge enhancement to current PCI that is also fully backward compatible in terms of both hardware and software. PCI-X is a 64-bit-wide bus (see Figure 8-10). Its slots will accept regular PCI cards. The real bonus of PCI-X is its much enhanced speed. The PCI-X 2.0 standard features four speed grades (measured in MHz): PCI-X 66, PCI-X 133, PCI-X 266, and PCI-X 533.
Figure 8-10 PCI-X slot
The obvious candidates for PCI-X are businesses using workstations and servers, because they have the “need for speed” and also the need for backward compatibility. Large vendors, especially in the high-end market, are already on board. HP, Dell, and Intel server products, for example, support PCI-X. A quick online shopping trip reveals tons of PCI-X stuff for sale: gigabit NICs, Fibre Channel cards, video adapters, and more.
Mini-PCI
PCI has even made it into laptops in the specialty Mini-PCI format (Figure 8-11). You’ll find Mini-PCI in just about every laptop these days. Mini-PCI is designed to use low power and to lie flat—both good features for a laptop expansion slot. Mini-PCI returns in Chapter 21, “Portable Computing.”
Figure 8-11 Tiny card in Mini-PCI slot. See the contacts at the bottom of the picture?
PCI Express
PCI Express (PCIe) is the latest, fastest, and most popular expansion bus in use today. As its name implies, PCI Express is still PCI, but it uses a point-to-point serial connection instead of PCI’s shared parallel communication. Consider a single 32-bit chunk of data moving from a device to the CPU. In PCI parallel communication, 32 wires each carry one bit of that chunk of data. In serial communication, only one wire carries those 32 bits. You’d think that 32 are better than one, correct? Well, first of all, PCIe doesn’t share the bus. A PCIe device has its own direct connection (a point-to-point connection) to the Northbridge, so it does not wait for other devices. Plus, when you start going really fast (think gigabits per second), getting all 32 bits of data to go from one device to another at the same time is difficult, because some bits get there slightly faster than others. That means you need some serious, high-speed checking of the data when it arrives to verify that it’s all there and in good shape. Serial data doesn’t have this problem, as all of the bits arrive one after the