Datasheet

Chapter 1

Personal Computer System Components

Identifying Purposes and Characteristics

of Processors

Now that you’ve learned the basics of the motherboard, you need to learn about the most

important component on the motherboard: the CPU. The role of the CPU, or central pro-

cessing unit, is to control and direct all the activities of the computer using both external

and internal buses. It is a processor chip consisting of an array of millions of transistors.

Intel and Advanced Micro Devices (AMD) are the two largest PC-compatible CPU manu-

facturers. Their chips were featured earlier in Table 1.1 during the discussion of the sockets

and slots in which they ﬁt.

The term chip has grown to describe the entire package that a technician

might install in a socket. However, the word originally denoted the silicon

wafer that is generally hidden within the carrier that you actually see. The

external pins you see are structures that can withstand insertion into a

socket and that are carefully threaded from the wafer’s minuscule con-

tacts. Just imagine how fragile the structures must be that you don’t see.

Older CPUs are generally square, with contacts arranged in a pin grid array (PGA). Prior

to 1981, chips were found in a rectangle with two rows of 20 pins known as a dual inline

package (DIP); see Figure 1.27. There are still integrated circuits that use the DIP form fac-

tor. However, the DIP form factor is no longer used for PC CPUs. Most CPUs use either the

PGA or the single edge contact cartridge (SECC) form factor. SECC is essentially a PGA-type

socket on a special expansion card.

FIGURE 1.27 DIP and PGA

DIP (Dual In-line Package)

PGA (Pin Grid Array)

As processor technology grows and motherboard real estate stays the same, more must

be done with the same amount of space. To this end, the staggered PGA (SPGA) layout was

developed. An SPGA package arranges the pins in what appears to be a checkerboard pat-

tern, but if you angle the chip diagonally, you’ll notice straight rows, closer together than

the right-angle rows and columns of a PGA. This feature allows a higher pin count per

area. Intel and AMD are migrating toward the use of an inverted socket/processor combi-

nation of sorts. As mentioned earlier, the land grid array (LGA) packaging calls for the pins

to be placed on the motherboard, while the mates for these pins are on the processor pack-

aging. As with PGA, LGA is named for the landmarks on the processor, not the ones on the

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