Buying a CPU/Processor for a Home-Built Computer

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Buying a CPU/Processor for a Home-Built Computer

When building a computer at home, one of the major decisions to make is which CPU to install. CPUs (central processing units), also known as processors, have a large role in determining how efficiently and effectively the computer runs software, and even the kinds of software it can support. Processors receive instructions from software and perform logical, arithmetical, and input/output tasks, thus enabling a system to run.

There are numerous CPUs available on the market, for everything from entry-level computers to cutting-edge gaming or workstation computers. It is important to find a CPU that is compatible with the rest of the computer system: one that is more sophisticated than the rest of the components cannot be properly supported, while one that is not powerful enough slows down the entire computer. As processor technology is ever-evolving, buyers should research in advance which models are most suited to their particular needs and expectations. In general, finding the right CPU involves balancing the right set of specifications with a price that fits one's budget.

Competing CPU Manufacturers

There are two major CPU manufacturers competing on the market: Intel and AMD. Both have a range of processors, from budget versions to high-end gaming and workstation models. While AMD CPUs are generally more affordable than Intel, tight competition between the two companies keeps their product lines relatively comparable. In fact, for basic computing tasks, the difference is little-to-none. Where higher-performance programs are concerned, AMD or Intel CPUs excel in different areas, so buyers should research the strengths and weaknesses of the latest developments.

One consideration when choosing between Intel and AMD is compatibility with the motherboard. When building a computer from scratch, this may not be an issue, but if the buyer already has a motherboard, they need to check which brand it is fitted for. An Intel processor cannot fit on an AMD board, and vice-versa. Motherboard costs also differ by manufacturer; therefore, they should also be factored in, when applicable, for a realistic picture of a particular CPU's expenses.

Motherboard Sockets

The socket is where the CPU attaches to the computer's motherboard. As mentioned above, these are brand-specific, but each brand also has a few different types of sockets. They evolve over time, and some sockets, but not all, are backwards-compatible, meaning they fit certain earlier models. For a given socket, there is a range of compatible processors, in which lower-priced versions are generally slower. This is a consideration for buyers who may want to upgrade their processor in the near future: they can look at the other available processors compatible with that socket and get an idea of what kinds of upgrades are feasible.

Processor Features

The most important specifications to consider when shopping for a CPU are its features: the number of cores, its clock speed, and whether it has hyper-threading capabilities. Buyers should bear in mind that not all software is equipped to support the capabilities of high-end processors, and that for single-thread-encoded applications, there is no difference at all. However, there is an increasing number of multi-threaded applications that can benefit from a more powerful CPU.

Number of Processor Cores

One of the most important CPU specifications is the number of cores it has. A processor can only handle one thread at a time. Manufacturers have dealt with this issue by adding more CPUs to the microchip, allowing for multiple threads to be processed simultaneously. Dual-core processors have two CPUs, quad-core have four, and so on.

Dual-core processors are standard, and those with four or more cores are increasingly available. At first glance, the more cores a processor has, the more tasks it can perform simultaneously, leading to faster running speeds and better multitasking. However, there are other factors that must be taken into consideration, including clock speed and what is known as hyper-threading or simultaneous multi-threading, which are discussed below.

The processor's job is to execute logical, mathematical, and input/output tasks assigned to it by a software program. Each sequence of programmed instructions is called a thread, which are allocated processing time by the operating system scheduler. The processor carries out the threads in order for the computer to run the programs.

Processor Clock Speed

Clock speed is a second important factor affecting processor performance. This figure, measured in gigahertz (GHz), expresses the number of billions of times per minute the CPU clock pulses. The processor needs a certain number of clock pulses to complete a task, and the faster the clock speed, the more instructions it can complete in a second.

Clock speed needs to be considered in context with the other processor specifications. With multi-core processors, for instance, the clock speeds stack up: a quad-core 3GHz CPU is much more powerful than a dual-core 3.3GHz CPU. And, with the development of hyper-threading, discussed below, clock speed becomes even more complicated to interpret, since some hyper-threading CPUs can outperform individual processors with more cores and faster clock speeds.


Overclocking involves making certain adjustments so that a processor runs faster than its specifications indicate. This can be accomplished in a number of ways, including altering the computer's clock rate, modifying the CPU multiplier and memory timings, and more. In general, overclocking involves a greater energy expenditure, which generates more heat; this issue needs to resolved in order to ensure the CPU's proper functioning.


Intel has developed hyper-threading technology, which uses a single core to process multiple threads. It does this by switching threads often enough to create the illusion that they are running simultaneously. To give an example of how this affects performance, a quad-core CPU with hyper-threading capability may be able to process up to eight threads, whereas a quad-core CPU with individual processors can only process four. While the former may not necessarily be able to work at twice the speed, this is still a significant boost to the processor's capabilities.

Additional CPU Considerations

While the above-mentioned features are crucial when deciding on a processor, there are additional specifications that indicate performance and features that enhance versatility and power.

Integrated Graphics

Processors that feature integrated video technology on the die (chip) itself allow users to have quality graphics without a discrete graphics card. This is important for applications like photo editing or transcoding video. On the other hand, users who plan to do 3D gaming, or who opt for a high-end CPU which does not include integrated video technology, need to purchase a discrete card.

Processor Cache

A CPU's cache is a certain amount of memory that it has for regularly-used information. A processor cache has three levels: L1, L2, and L3. L1 is the primary cache, where instructions are stored and quickly retrieved to be fed to the microprocessor. L2 gives instructions to L1, and has a slower memory, while L3 feeds to L2. In general, the more memory in each level of a CPU's cache, the more efficient it is.

Boost Potential

Processors with boost potential do not have strictly-regulated clock speeds. If there is sufficient power and the chip is cool enough, it can increase its speed to "boost" its power for a time. Intel calls this feature "Turbo Boost", while AMD refers to it as "Turbo Core". The specifications should indicate the regular and boosted speed, and buyers can expect higher prices for more boost.

Information Processing

The amount of information a CPU can process at one time is indicated in bits, where one bit equals eight bytes. For example, a 64-bit CPU processes 64 bits, or eight bytes, of information, at one time. This number is important with reference to software, which is designed to support a certain amount of information processing.

How to Buy a CPU/Processor on eBay

eBay has a wide selection of new, used, and refurbished processors at competitive prices. To start searching, go to the eBay home page and enter keywords like "quad-core Intel processor" into the search bar. You can refine your search results by then selecting specifics like series, socket type, clock speed, price range, and more.

Once you've found a processor you're interested in, be sure to read the item description thoroughly, as well as the postage and payments information. If you have any questions, you can contact the seller through eBay. It is also a good idea to research the seller: have a look at the feedback score, and read comments left by past customers who've bought CPUs or similar components. This gives you a sense of the seller's reliability and knowledge, so you can buy with confidence. Once you've completed your transaction, you can leave your own constructive feedback for them.


Central processing units (CPUs), or processors, are the centre for information processing in a computer. They perform tasks as instructed by a computer program, effectively enabling it to run. For this reason, processors are vital to a computer's ability to run software quickly and effectively. When building a computer, consumers have their choice of CPU; understanding the various product specifications helps them decide which processor is right for them.

The most important specifications revolve around processor speed and performance. The three considerations are the number of cores, clock speed, and whether the cores have hyper-threading capability. Individual cores process one thread at a time; having multiple cores increases multitasking, and the faster the clock speeds, the more tasks can be processed per second. Hyper-threading mimics simultaneous processing of multiple threads in a single core. Other factors to consider are manufacturer, cache size, the amount of information that can be processed, and features like boost potential and integrated graphics technology.

Buyers should research the latest CPU models to find one that meets their criteria for specifications and cost.

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