Datasheet

Identifying Components of Motherboards
13
you might wish to research these slots for your own edification and to be prepared, should
you find yourself face to face with such a beast in the field. PC Card buses, such as PCMCIA,
are related more to laptops than to desktop computers and are covered in Chapter 4.
PCI Expansion Slots
Many computers in force today contain 32-bit Peripheral Component Interconnect (PCI)
slots. They are easily recognizable because they are short (around 3 inches long), compared
to the classic ISA slot, and usually white. PCI slots can usually be found in any computer
that has a Pentium-class processor or higher. PCI expansion buses operate at 33 or 66MHz
over a 32-bit (4-byte) channel, resulting in data rates of 133 and 266MBps, respectively,
with 133MBps the most common, server architectures excluded. Servers often feature
64-bit slots as well, which double the 32-bit data rates.
PCI slots and adapters are manufactured in 3.3 and 5V versions. Universal adapters are
keyed to fit in slots based on either of the two voltages. The notch in the card edge of the com-
mon 5V slots and adapters is oriented toward the front of the motherboard, and the notch in
the 3.3V adapters toward the rear. Figure 1.6 shows several PCI expansion slots. Note the 5V
32-bit slot in the foreground and the 3.3V 64-bit slots. Also notice that a universal 32-bit card
fits fine in the 64-bit 3.3V slot.
FIGURE 1.6 PCI expansion slots
AGP Expansion Slots
Accelerated Graphics Port (AGP) slots are known mostly for video card use and are
steadily being supplanted by PCI Express adapters. In the past, if you wanted to use a
high-speed, accelerated 3D graphics video card, you had to install the card into an exist-
ing PCI or ISA slot. AGP slots were designed to be a direct connection between the video
circuitry and the PC’s memory. They are also easily recognizable because they are usually
brown, are located right next to the PCI slots on the motherboard, and are slightly shorter
than the PCI slots.
Another landmark to look for when identifying later AGP slots is the often alternate-
colored shell surrounding the slot with an extension toward the front of the system that
snaps into place at the “rear” of the adapter. It is necessary to pull the extension away from
the adapter before removing it from the slot. Figure 1.7 shows an example of an AGP slot,
along with a PCI slot for comparison. Notice the difference in length between the two.
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