More on CPUs


The Processor

Earlier, we discussed CPU (processor) basics. Here we will go into more detail. In the image below, you can see a view of the top of a processor. This particular processor is an AMD Sempron 2800+. Of the entire piece below, the 'actual' processor is only the little gray piece in the center. Since there are so many electrical connections on the tiny processor, it has to be mounted into the larger assembly. If it were not, the interface connections/contacts would have to be approximately the size of a human hair and would not be reliable in the real world.

In the following image, you see the bottom of the same processor. This processor fits 'socket A' motherboards. It has 462 pins. This is a relatively low pin count and will likely soon be phased out.

The following image shows a newer Sempron processor. On the newer processors, the processor has a heat spreader to more efficiently transfer the heat to the heatsink. The processor is still a fraction of the size of the processor module. This processor module has 940 pins (socket designated as AM2). The extra pins are used for better (faster) communications between the processor and the memory as well as other peripheral ICs on the motherboard.

Installing the Processor into the Socket

Below, you see a 'socket A' motherboard. If you look closely in the following images, you can see that it says 'socket 462'. That's used interchangeably with 'socket A'. Along the far side of the socket, you can see a long metallic handle. That handle is used to lock/unlock the socket. As you can see, the CPU has a lot of pins. To keep a good contact on the pins, there has to be a fair amount of clamping pressure on each of the pins. When you clamp down on any pin in any socket, it takes a fair bit of force to pull the pin from the socket. Even if it only takes a single ounce of force for each pin, the force to remove the CPU would be nearly 30 pounds. Simply pulling the CPU from a standard type socket, would destroy it. To get good contact pressure AND allow acceptable removal/insertion force, the socket has a slide mechanism that disengages the contacts. This type of socket is called a Zero Insertion Force (ZIF) socket. When the handle is down, the pins are clamped. When the handle is up, the pins are released.

This next image shows the handle in the 'free' position. When the handle is in this position, inserting the CPU should take virtually no force. Ideally, gravity should provide enough force to fully seat it. Typically, it takes a very slight force (only a few ounces of force) to seat it. If it takes any more than that, pull the processor and check for bent pins. A bent pin on a processor is a very bad thing. Often, they're made of a relatively brittle material and if badly bent will break when straightened. If a pin gets bent, very slowly straighten it. If it breaks, there is little chance that the processor will work. Also, the manufacturer will not warranty a processor with broken pins. For that reason, you must be very careful when handling the processor. It should either be in the original shipping container or in the socket.

Here, you can see the processor in the unlocked socket. If you notice, there is a triangle in the corner of the CPU. This helps you to get it properly oriented in the socket. In the previous images, you can see that the socket has missing holes on the corners along one edge and the CPU has corresponding missing pins.

Here (below), we see the processor locked down into the socket.

The Thermal Pad

The HeatSink and Fan (HSF) below has a thermal pad covering the target area for the processor. The thermal pad is designed to conduct heat from the CPU to the heatsink. It is used to fill in tiny imperfections in the two components that would otherwise be filled with air (which is not an effective thermal conductor).

Don't try this at home... I removed the heatsink after mounting it to show you what happens to the thermal pad. I didn't run the processor with this thermal pad. If I would have, the indention would be much deeper and you would have been able to see the copper of the heatsink through it. When I install the processor later, I will be removing the pad to use a better, thermally conductive compound. After mounting the HSF onto the processor, you can not remove it. If you do remove it, you must either replace the pad or use some other thermally conductive material between the sink and the CPU. If you try to reuse the pad, it's unlikely that you will get adequate thermal conductivity from the used pad and the processor may overheat (and possibly fail).

Mounting the Heatsink and Fan

Below, you can see the CPU and socket from the side. Notice that the socket had a raised area on the right side of the picture. This area houses part of the mechanism that locks/unlocks the CPU. If you look at the HSF, you can see a corresponding cutout.

If you look at the angle of the HSF vs the processor, you can see that the HSF isn't sitting level. That's because the cutout in the heatsink is on the wrong side. It IS possible to clamp the HSF to the processor like this but the processor will not be in contact with the HSF and will overheat (and probably fail). When mounting the HSF be sure to set it the right way.

Here, the HSF is oriented properly.

In the next image, you see the HSF in place but it's not locked down. To maintain good physical contact between the HSF and the processor, a spring-loaded clamp is used. On the socket, there are three protrusions. These correspond to three slots in the spring clamp. The other side of the socket is made the same way.

To get the spring clamp into place you use a screwdriver as shown below. You gently pry the clamp outwards so that you can get over the protrusions on the socket. Then you slowly release it so that the clamp falls into the notches on the protrusions.

Above and below, you can see the clamp in place from 2 different angles. Make sure that you catch all three protrusions. If you don't, the clamp may break the socket which may render the motherboard useless.

CPU Specifications

Model: AMD Sempron 2800+
This tells you that the processor is manufactured by AMD and is supposed to be equivalent to a 2.8G Celeron (rated at 2800MHz+ or 2.8GHz+). AMD processors run at significantly slower clock speeds than Pentium processors that can do approximately the same work per unit of time. This processor has an internal clock speed of 2.0GHz but is approximately as fast as a Celeron running at 2.8GHz. The Athlon line of AMD processors have their speeds compared to Pentium 4 processors.

Core: Thorton
The 'core' is the name given to a particular architecture. Some of the AMD cores are the Thoroughbred, the Barton, the Applebred and the Clawhammer.

Operating Frequency: 2.0 GHz
As mentioned above, this is the internal clock frequency of the processor.

FSB: 333MHz
This is the operating frequency of the Front Side Bus. Higher speeds mean better performance.

Cache: L1/64K+64K; L2/ 256KB
This is the amount of on-board memory. It's relatively small compared to the system memory but since it's on the die (on the piece of silicon) with the processor, data can be transferred more efficiently to it.

Voltage: 1.65V
This is the stock operating voltage of the processor. Sometimes, the operating voltage is increased when someone wants to run the processor at faster than stock speeds. This often works but causes the processor to generate more heat and will therefore cause it to run hotter. If the processor isn't kept cool, it could fail. Newer processors often have thermal protection but it's no guarantee that the processor will not fail if it overheats.

Process: 0.13Micron
This is the minimum size of the transistors (and other components) on the die. Newer processors have ever decreasing sizes. Smaller sizes allow the processors to be smaller and will allow more to fit on the silicon wafer. I will show you a wafer later on this page.

Socket: Socket A
This is the socket in which the processor fits.

Silicon Wafer:
Below, you can see a 5" silicon wafer. As you can see, there is a repetitive pattern on it. Each segment of the pattern is an individual processor. While I don't know exactly what the device is, it IS some sort of processor. Silicon wafers are relatively expensive to produce. This means that the manufacturer tries to get as many components on the wafer as possible. When the device is large, fewer can be manufactured per wafer. Above, the 'process' was specified as .13 microns. The newer process is specified as 0.09 microns. This means that the size of the transistors and other components are smaller than 0.09 micrometers (millionths of a meter). With the newer process, the manufacturer can produce more processors per wafer and therefore reduce the cost of each processor.

Click HERE to see a very large view of the wafer (scanned at 4800dpi). If your browser displays it properly, you will not be able to see all of it at one time. On my monitor, it looks to be approximately 3 feet across. If your browser resizes it, hold your mouse over the image until the browser resize button appears in the lower right-hand corner of the image. When the button appears, click it. When the image appears at full size, you will only be able to see a small corner of it (similar to that which you see in the second image below). Use the scrollbars to view other areas of the wafer.

Below is an enlarged view of a single processor.



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