Remove the processor from its packaging and examine it closely to make sure that no pins are bent. A new processor should never have bent pins. If one or more pins are bent, that's certain proof that you were sold a used or repackaged processor. Do not attempt to straighten bent pins. Return the processor and insist on a replacement processor in original factory shrinkwrap.

The processor fits a Zero Insertion Force (ZIF) socket on the motherboard. To prepare the socket to receive the processor, lift the small lever on one side of the socket to the vertical position.

Examine the socket to determine which corner is pin 1. pin 1 may be indicated by a small diagonal cutout on the socket, by a dot or arrow, by a number 1 printed on the socket or motherboard itself, or by other similar means. Once you have located pin 1 on the socket, locate pin 1 on the processor, which is also marked clearly.

Carefully align the processor with the socket, making sure that pin 1 on the processor corresponds to pin 1 on the socket, and then drop the processor into place, as shown in Figure 28-13. We say "drop" rather than "press" because the processor should seat fully in the socket with little or no resistance (that's why it's called "Zero Insertion Force"). If you encounter resistance, either the pins are misaligned or the ZIF lever is not fully vertical. Don't force the processor into the socket, because those tiny pins are very easy to bend, which effectively destroys the processor. When the processor is seated properly, its bottom should be flush against the top of the socket.

Figure 28-13. With the ZIF arm fully raised, carefully align the processor, making sure pin 1 on the CPU corresponds to pin 1 on the socket, and drop the processor into place

With the processor fully seated, pivot the ZIF lever down until it is parallel to the motherboard to lock the processor into place (Figure 28-14). You may encounter resistance while closing the lever, which is normal. Continue pressing the level down until it snaps into place. Don't press too hard, though. If the lever seems not to want to seat, you may have the processor misaligned.

Figure 28-14. With the processor fully seated, lower the ZIF socket arm until it snaps into place parallel to the motherboard and is secured by the plastic latch

Before installing the heatsink/fan unit, use a paper towel to polish the top of the processor to a mirror-like surface to remove fingerprints and other residue (Figure 28-15). Intimate contact between the processor and heatsink is critical to ensure proper cooling. Even a fingerprint can interfere with heat transfer.

Figure 28-15. Polish the processor carefully before applying thermal compound

Retail-boxed Intel Pentium 4 processors include a heatsink/fan unit and a pre-measured amount of thermal compound in a syringe. After you have polished the top of the processor, use the supplied syringe to deposit the full amount of supplied thermal compound in a small pile at the center of the processor, as shown in Figure 28-16. Although it appears that using all of the supplied thermal compound will make a mess, you need to apply all of it to ensure proper cooling.

Figure 28-16. Apply the supplied thermal compound as a small pile at the center of the processor

Lower the heatsink/fan unit gently into position. Keep the heatsink as level as possible as you lower it into contact with the processor (Figure 28-17). The goal is to press the heatsink gently into place, thereby spreading the thermal compound evenly over the surface of the processor to ensure good heat transfer. If you tilt the heatsink as you're moving it into place, most of the thermal compound may be shifted to one side of the processor. When the heatsink/fan unit is properly in place, it should be sitting level within the heatsink retention mechanism on the motherboard.

Figure 28-17. After applying thermal compound, align the heatsink squarely on top of the processor

The heatsink/fan unit includes two spring-steel retaining brackets that clamp the heatsink into tight contact with the processor. Align each bracket so the central hole fits over the corresponding tab on the heatsink/fan retention mechanism, and then use both thumbs to press the two ends of the retaining bracket until they snap into place against the heatsink retention mechanism (Figure 28-18). It may require substantial force to seat the bracket, so don't be afraid to press hard. With some brackets, it's easier to seat one side first while it's not under tension and then press down the opposite side until it snaps into place. Make certain that both ends of both brackets are secured. You don't want the heatsink/fan to come loose, particularly if the motherboard is mounted vertically (Figure 28-19).

Figure 28-18. Snap both heatsink support brackets over the matching connectors on the heatsink retention mechanism

Figure 28-19. When the retaining brackets are installed properly, the hole on each end snaps into the corresponding tab on the heatsink retention mechanism

The Pentium 4 CPU fan connects to a motherboard power header. Most motherboards, including the D845WNL, include two or more such power headers, but those headers are not fully interchangeable. All of them supply the same voltage on the same pins, and any can be used to power any fan, but the CPU fan header is designed to report the speed of the CPU fan to the motherboard, where that information can be used by a hardware monitoring utility. Connect the CPU fan header to the specific motherboard power header intended for it. Other motherboard power headers can also report fan speeds to the motherboard, and are intended to power supplemental chassis fans. (See Figure 28-20.)

Figure 28-20. Connect the heatsink fan power lead to the motherboard CPU fan header