Central Processing Unit (CPU)

What is a CPU?

The Central Processing Unit (CPU) is responsible for interpreting and executing most of the commands from the computer's hardware and software. It is often called the "brains" of the computer. 

The CPU is Also Known As: processor, microprocessor, central processor, "the brains of the computer"

The modern day CPU has hundreds of little round contacts around the bottom surface, as seen in the top image. These contact with pins on the motherboard, inside a socket specially designed for the CPU. Each motherboard has a specific socket type, and only CPU's of that socket type are compatible with that board.

In the older CPU's, the contacts used to be on the motherboard and the pins were on the CPU. Fortunately this has now changed, as many people discovered the hard way that putting your CPU in the wrong way and bending the pins was a good way to throw away a couple of hundred dollars.

In a fully assembled system, you wont be able to see the CPU when you open the case. It will be covered up by the heatsink and fan cooling system on top of it. Without this cooling system, a CPU can heat up to many hundred degrees in a matter of seconds. These sort of temperatures can easily destroy a processor chip, and in some cases, even cause them to explode.

In this internal image of a computer system, you can see in the upper right region of the motherboard, just below the four RAM rails, there is a large, black, square-shaped object with a fan inside. This is part of the cooling system for the CPU. At the top is the fan and beneath that there is a heatsink. This is a light metallic structure with several thin fins that absorbs heat from the CPU beneath it and allows it to be dispersed by the air blown down through them by the fan on top. The CPU itself is fastened into the motherboard beneath this cooling system.

CPUs come in various different designs, though from the outside, most appear very much the same. As mentioned before, each CPU is designed to fit into a specific type of motherboard socket, and so they are incompatible with any other socket-type board. CPUs also have various different operating designs, some with single cores and others with multiple cores. CPU's with more than one core are capable of carrying out more than one process at a time. In short, they can multitask.

CPU's are also rated with various different speeds, which are measured in Gigahertz (Ghz). Basically the higher the Ghz rating on a processor, the faster it can put through data and information. However processors with multiple cores may have a slower Ghz rating than a single core processor and still be a faster chip, since they can put through more data at a time.

Cpu installation guide

Processors, can be different, so you don't want to swap out a Pentium 4 with a AMD Sempron . They are not compatible, unless you plan to build an entirely new system. If you are unsure your new CPU will fit in your current system, Go to http://www.softpedia.com/get/System/System-Info/CPU-Z.shtml the program CPU-Z will tell you everything about your computer. Remember to verify that the socket on your motherboard will fit the new CPU.  

After laying the motherboard out on a clean work surface, remove the plastic cover that shields the LGA775 socket's pins from harm. Be careful not to bend or otherwise disturb these pins—they need to line up just right with contact points on the base of the CPU.

With the plastic guard removed, you'll easily be able to unclip the lever that holds the socket's CPU retention mechanism in place. Flip this retention bracket back on its hinges to expose the socket in full.

Modern CPUs are keyed to ensure that they can only be inserted into a socket one way, just like a puzzle piece, so you should have no problem dropping your processor into the socket. LGA775 processors, for example, have little indents along opposing edges that line up with protrusions in the socket. If your CPU struggles to slide smoothly into the socket, chances are you've got it oriented the wrong way.

Once the processor is sitting comfortably in the socket, flip the retention bracket back down and use the lever to clamp it into place. This secures the CPU to the motherboard.

With the processor installed, we can move onto the application of thermal compound. Some folks like to apply thermal paste before dropping the processor into the motherboard, but I find that tends to be a little messier without making things any easier.

Before slathering thermal compound all over our processor's exposed cap, it helps to make sure that cap is nice and clean. Gently brush the cap with a Q-Tip dipped in rubbing alcohol to rid it of any dust or oils that it may have picked up from your grubby carefully manicured fingers during the installation process.

Next, we apply thermal compound. Most retail processors that come packaged with coolers will already have thermal compound applied to the base of the heatsink. If yours does, you can skip this step and proceed directly to heatsink installation. However, we recommend applying thermal compound yourself. Thermal compound works best as a very thin layer between the CPU and heatsink, and most heatsinks that come with paste pre-applied use a thicker layer than is optimal.

You really only need a small dab of thermal compound to ensure complete coverage for the CPU. The dollop pictured above is more than enough, and it's best squeezed onto the center of the processor's metal cap.

Next, spread the thermal compound over the processor, ensuring complete and even coverage. Some thermal compounds come with plastic spreaders, but you can also use a credit card or even a finger wrapped in a plastic bag. What you want to end up with here is a relatively smooth layer that's just thick enough to completely cover the processor.

Don't worry about getting a little paste on the CPU retention bracket; it won't do any harm there. You will want to clean up any compound that makes its way onto the motherboard or its surface-mounted components, though. A Q-Tip dipped in rubbing alcohol should do the trick.

Once the processor is glazed with compound, we can turn our attention to the heatsink. If you've elected to do your own thermal compound application, you'll want to make sure that the heatsink's base is scrubbed clean. Rubbing alcohol usually gets the job done, but some heatsinks are slathered with particularly gooey, clingy, or otherwise uncooperative thermal interface materials. It may be necessary to break out more noxious substances, such as nail polish remover, to restore the base of the heatsink to a bare metal shine.

Be careful not to mar the base of the heatsink when removing any thermal compound that may cover it. Some heatsinks need to be scraped clean of thermal compound, and it's best to scrape with something plastic rather than a metal tool that will gouge the heatsink's surface.

 With our system's processor blanketed by a thin veil of thermal compound and our heatsink's base scrubbed clean, it's time to mate the two together. Before dropping the heatsink into place, ensure that all four of the heatsink's plastic retention posts are rotated clockwise into their installation position. Next, place the heatsink on top of the CPU, lining up the four retention posts with corresponding holes in the motherboard.

When the posts are lined up, depress the black plastic tabs one by one to lock the heatsink into place. You should hear an audible click as each post locks into place.

Since the area around a modern motherboard's CPU socket is often crowded with tall capacitors, heatsinks, and elaborate heatpipe arrays, I find it's best to depress the retention post that's least accessible first. The post directly opposite that one should be next, followed by the remaining two in whichever order you desire.

After locking the heatsink into place, plug its fan into the appropriate header on the motherboard. The CPU fan header is usually right next to the socket, but if you can't find it, your motherboard manual should have a map highlighting its location.

Note whether the heatsink you're using features a fan with a three- or four-pin header. That information will come in handy when we jump into the BIOS to configure fan speed control, since some motherboards can't auto-detect fan types.