CPU Unit

How Do CPU's Work?

The CPU of a computer, or central processing unit, is frequently compared to the human brain since it's the central control of the computer. The CPU performs computer operations by rapidly executing program instructions. The speed of the CPU plays a large part in determining the power of a computer. Each new generation of microprocessors features a more powerful CPU that can execute instructions more quickly than the previous generation.

The working of the CPU is defined as a three-step process. First, an instruction is fetched from memory. Second, the instruction is decoded and the processor figures out what it's being told to do. Third, the instruction is executed and an operation is performed. These three steps repeat in a cycle that begins again with the CPU fetching the next instruction. The steps are referred to as the instruction cycle of the CPU.

The CPU uses a program counter to keep track of which instruction to fetch next. The counter is the address of the memory location that holds the next instruction to be executed. It's stored in a register, which is a dedicated memory location in the CPU itself. The program counter is incremented to point to the next instruction after each fetch in the instruction cycle.

Operations Performed by a CPU

The CPU executes instructions that perform a set of basic operations. There are arithmetic operations like addition, subtraction, multiplication and division. Memory operations move data from one location to another. Logical operations test a condition and make a decision based on the result. Control operations affect other components of the computer. These basic types of operations, executed very quickly, allow a computer to perform a wide range of functions. The exact number of operations supported by a CPU depends on its architecture.

How CPU's Use Memory

Computer memory refers to the area where data and programs are stored. Memory is not part of the CPU, but the CPU must interact closely with it. There are two types of computer memory: primary, or main, and secondary. The CPU relies heavily on main memory (RAM) for storing program instructions and the data the instructions operate on.

Main memory (RAM) is temporary in nature and only holds instructions and data for a program while the program is executing. Secondary memory is the more permanent storage provided by hard drives and flash drives.

Types of CPU's

There are two primary manufacturers of computer microprocessors. Intel and Advanced Micro Devices (AMD) lead the market in terms of speed and quality. Intel's desktop CPUs include Celeron, Pentium and Core. AMD's desktop processors include Sempron, Athlon and Phenom.

Intel makes Celeron M, Pentium M and Core mobile processors for notebooks. AMD makes mobile versions of its Sempron and Athlon, as well as the Turion mobile processor which comes in Ultra and Dual-Core versions. Both companies make both single-core and multi-core processors.

Each processor has a clock speed which is measured in gigahertz (GHz). Also, a processor has a front side bus which connects it with the system's random access memory (RAM.) CPUs also typically have two or three levels of cache memory. Cache is a type of fast memory which serves as a buffer between RAM and the processor. The processor's socket type determines the motherboard type where it can be installed.

PGA CPU

PGA Socket on the motherboard

LGA CPU

LGA Socket on the motherboard

BGA CPU and the socket it fits into

CPU Sockets

The CPU socket on the motherboard locks the central processing unit into place, preventing it from moving or being damaged. It also establishes the connection between the CPU and board so data can transfer to the CPU for processing and return. Different models and types of computers require different types of CPU sockets, as not all CPUs are compatible with every kind of socket. The main difference between CPU sockets is how and where they connect to CPUs. The CPU socket determines the type of CPU you can use.

PGA Socket

A pin grid array (PGA) socket is usually a square package made up of a number of holes in an array. The CPU itself has the pins that insert into the socket. The arrangement of pins on the CPU must correspond to the slots on the socket; if not, the CPU will not connect properly to the board. To secure a CPU into a PGA socket, you have to press down until spring contacts lock it -- however, if you do not line up the pins properly, you may bend or damage them.

LGA Socket

A land grid array (LGA) socket is essentially the opposite of a PGA socket. Instead of having the pins connected to the CPU, they’re connected to the socket itself while the CPU has slots with connectors. To lock a CPU into an LGA socket, you have to line up the pins and apply a small amount of pressure. LGA sockets are less fragile overall than PGA sockets, and you can also solder down the package using surface mount technology.

BGA Socket

A ball grid array (BGA) is another variant on the PGA socket -- but instead of pins, a BGA socket has copper pads which that are soldered to the package. This means that you do not have to worry about damaging any of several hundred pins, especially as pin-chip architecture designs CPUs with pins closer and closer together. This also means there's less distance for data to travel, so there's less of a chance that the signals will distort.

What to Consider When Buying a CPU

Cores

Less than a decade ago, all processors came with a single core. Nowadays single-core processors are the exception and not the rule. Multi-core processors have become more popular as their availability has become increasingly common and software has been designed to utilize multi-core technology. From dual-core to eight-core processors, there are a number of options to choose from. When deciding how many cores are needed, first it is necessary to understand what “multiple cores” means.

When processors were running on a single core, that one core was responsible for handling all the data sent to the processor. As more cores are integrated into a processor, those cores are able to split up the processor’s tasks. This makes the processor faster and more efficient. However, it is important to remember that a processor can only perform as well as the existing software running it. If the software is only able to utilize three of the eight cores, then five cores are going to be unused. To maximize cost and use, it is best to match system requirements with core availability.

Cache

A processor’s cache is similar to the memory of a computer. A processor’s cache is a small amount of very fast memory that is used for temporary storage. This allows a computer to retrieve the files that are in the processor’s cache very quickly. The larger a processor’s cache, the more files it will be able to store for that quick retrieval.

Socket Compatibility

Socket compatibility is a primary concern when it comes to buying a processor. The socket compatibility enables the interface between a motherboard and its CPU. If a motherboard has already been acquired, make sure that the processor installed is compatible with the motherboard’s socket. Alternately, when building a computer around the processor, make sure that the motherboard is compatible with the existing processor.

Frequency

The frequency of a CPU, measured in hertz (Hz), is the speed at which it operates. In the past, a merely faster frequency equaled better performance. This is not necessarily the case any longer. In some cases, a CPU running at a lower frequency may actually perform better than a processor running at a higher frequency due to the infrastructure of the CPU. It is important to look at a CPU’s “instructions per clock” in addition to the frequency of the CPU. While frequency is still a good indication of how quickly a processor can perform, it is no longer the only factor that impacts the actual speed of a processor.

Thermal Design Power

Processors generate heat. The thermal design power specification assigned to a CPU explains how much heat the processor is going to give off. This will directly affect the type of cooling device needed for a CPU. If the CPU does not come with a cooling device or if the cooling device provided is not used, a device must be installed that can cool the system sufficiently. Overheating is a primary danger to a computer’s componentry.

What Can cause a CPU to Fail?

Like any other electronic component, the CPU can die for simple reasons. Below are the items that you should minimize in the system if you want to lengthen a CPU’s lifespan.

Heat. A working CPU generates heat but if heat levels go beyond the normal threshold, the CPU can die from it. Again, never underestimate the power of fans. There’s a reason why extensive cooling systems are expensive. If possible, put the computer in an air-conditioned room so heat build up becomes slow.

Aging. Some processors can outlive all other components but most of the time, you can expect an old CPU to just give up anytime. If you have an older system (over 5 years old), the CPU can suddenly die even if it’s taken care of properly. The first component in the CPU assembly that usually gives up is the fan. Over time, this moving part simply reaches its natural limit and there’s nothing that you can do about it. There are millions of transistors in a CPU and if one of two stop working, the CPU may malfunction if it does a specific task. This one is difficult to check directly so if you’ve ruled out all possible causes, the only thing that you can do is to replace the CPU.

Undue stress or overclocking. CPUs are rated based on their clock speeds. Some CPUs are designed to allow faster clock speeds for enhanced performance but this comes at a price. Overclocking can add stress to the unit, shortening its overall lifespan in the process. In other words, you are trading longevity of the CPU for more processing power, which is not entirely bad. If you have the resources to get a faster CPU though, we suggest that you do so instead of overclocking.

Power surge or unstable voltage. Many of today’s processors are so reliable they can run continually for years without breaking down. However, if you are in an area with frequent lightning storm or unstable power lines, a power surge can effectively kill a processor, if not the rest of components in the motherboard. Try not to connect your computer directly to the wall outlet. If possible, use a surge protector to safeguard your computer from sudden power spikes.

Bad motherboard. A motherboard is a sophisticated interconnection of many different components and sometimes, even one bad capacitor can cause another component to fail. Try to do a visual hardware check on the motherboard and watch out for leaking or bulging capacitor. If you find one, there’s high probability that it’s causing the CPU to fail.

Symptoms of a failing CPU

Lock ups and overheating immediately before PC shuts down. If you noticed that your computer had lock up instances before the final crash, one of the things that you should consider is a bad CPU. It may have overheated causing the system to shut down automatically to prevent further damage. A CPU has a built-in fan to keep itself cool but if the fan fails for some reason, the CPU can temporarily overheat. This is one of the reasons why you should ensure that all fans in your computer are checked and cleaned once every year. Dust can sometimes choke fans so keeping it away regularly can make or break a system. If your CPU appears to suffer from frequent overheating, consider cleaning its fan first. If that won’t work, check the BIOS to see if there’s a way for you to lower its RPM. Doing so may have significant impact on performance, especially if you’re using your computer for graphics-intensive activities but it can also be the only effective remedy short of replacing the CPU.

Keep in mind that prolonged overheating can permanently damage the CPU. If you are 100% sure that the CPU is overheating (some motherboards have diagnostic tools to let you monitor the CPU’s temperature), find a way to lower the temperature down, or consult an expert how to fix it.

Beeping. As mentioned above, your computer runs a self check (POST) to verify if all the essential peripherals are working or not. If the test will find out that the CPU is not working, the boot up process will then be interrupted and the motherboard will produce a beeping sound. The beeps are actually codes that helps a technician identify the problem so make sure that you take note how many beeps there are. You can then search Google what the beep code means.

Charred motherboard or CPU. Severe overheating can melt or leave charred appearance on both the motherboard or the CPU itself. Try to remove the motherboard from the tower and disconnect the CPU to see if this is the case (steps provided below). If overheating was bad, the CPU may be damaged permanently. In this case, there’s nothing more that you can do about it. Simply replace it and go on with your life. Depending on the damage, the motherboard can also be rendered useless so make sure that you troubleshoot the motherboard too afterwards.

Troubleshoot a Failing CPU

A CPU either works… or not. If properly installed, a CPU will work until it dies, unless something drastic happens like a power surge, lightning strike, or severe motherboard damage. That said, if a CPU appears to be not working anymore, the best thing that you can do is to replace it. Period.

Check if the system is overheating. Before you consider the physical removal of the CPU and testing a new one, you must double check if the system is showing signs of overheating. These are some of the concrete steps that you can try:

Make sure that airflow is clear. Sometimes, extra cables inside the case can block important vents.
Keep the number of fans under control. Too many fans does not necessarily mean it’s better.
Check the fan or heat sink. Make sure the fan is working, and check the thermal compound between the CPU and heatsink. Thermal compound, also known as thermal paste and thermal grease, is a material used to fill the microscopic gaps between a computer's CPU and its heat sink. Thermal compound significantly increases the heat sink's ability to cool the CPU, allowing the CPU to run at a higher speed and improve system performance.

If nothing happens during boot up, that is, the display remains blue or black and you suspect a processor failure, you must do the following steps:

Check if the power LED light on the motherboard is on or off.
If the LED light is off, check for motherboard or power supply issues.
If the LED light is on, check if the processor fan spins when the system is powered on.
If the processor fan spins, you must do a swap test using another workable processor.

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