How To Buy A CPU (Processor)

The central processing unit serves as the main brain of your computer. While some modern graphics cards can do a fair amount of logical processing, the CPU takes the lion’s share of the workload. There is a lot going on underneath the hood of a CPU, but fortunately it can be broken down into a few overarching specs to make the selection process easier. This guide will focus on educating newcomers rather than looking at specific models so that they can have a fair idea of what the various specifications mean, how they factor into the performance of the CPU, and other things of which to be aware.

Intel vs AMD

The choice of manufacturer for CPUs has fewer options than many other components, but the implications of the choice are much more palpable. You can run almost any OS on modern CPUs, even the Mac OS, but which motherboard you can use is directly determined by the CPU. As far as which is better, the extreme high end is dominated by Intel CPUs. As you get below that, you can find options from both vendors. This does have a side effect of making the top end even more expensive due to a lack of competition, so the best price for performance hovers around the best AMD chips.


Processor Architecture, Sockets, and Chipsets

Every CPU is designed on an architecture that is made to interface with a specific socket. For example most of the Intel’s processors are made for the LGA 1150 socket, and many of the latest AMD chips are designed for the AM3+ socket. The pros and cons of each chipset are discussed in more detail in the motherboard buying guide. When looking at it from a CPU angle, if you already have a motherboard selected, then all you need to do is ensure whatever CPU you pick fits into the socket.

The architecture model of the CPU is ultimately one of the most deciding factors in its performance. The new Skylake architecture from Intel will give you your highest consumer performance levels. Ivy Bridge is the next step down, and it and its younger brother Sandy Bridge go in the same sockets. AMD changes the sockets for their CPUs less frequently, so an AM3+ will give you a wide variety of choices. The best bet here for performance is the FX line.

Cores and Threads

You will most likely find quad core CPU’s today, but there chips ranging from single cores all the way up to 80 cores (supercomputers). Effectively, a core is like multiple CPU’s existing within the same chip. It is an unfortunate fact that multiple cores and threads will not really provide any impact on any one program, as most applications are programmed to only utilize a single thread. That said, you will notice a boost in some programs, and multitasking is aided slightly by having more cores. For now, there is not much reason for a gaming rig to use anything above the common quad core processors for the few games that take advantage of multithreading and to prepare for the future.

What is Hyper threading?

Hyper-threading is the technology developed by Intel and released with the later versions of Pentium 4 CPUs, that were initialy released in 2000. However that generation of CPU’s didn’t go that well, not because the idea of hyper threading was bad and didn’t show any results, but because Intel didn’t manage to reach the high frequencies that they had hoped for.

Intel got back to the drawing board and later managed to release the technology on three families. Intel Core, Intel Core M and Intel Xeon.

Hyper threading is an ability of the individual core to execute two processes at the same time, some processes can be done simultaneously by the core and some can’t. No matter how fast your CPU is, when you have multiple programs running in the background, an individual processor core can only execute one instruction at a time. This delay is not always noticeable by the user, because the core itself is doing its job very fast, but the delay does exist and it is based on how the data from each program is fed to the processor. With non-HT CPU’s those data streams (threads) must be executed by the core individually, but when you have hyper threading, the core it self is splitting and assigning resources to two threads at once. Those threads are also called logical cores (virtual cores if you prefer, those cores do not physically exist ), and your operating system will recognize them as cores in your task manager, but do not be fooled, if you bought an i7 it is still a quad core that will be doing the actual execution.

In real life applications, hyper threading can be useful only if they support it. When it comes to office work, web browsing and watching movies you will not notice the benefits of hyper threading. However, if you are using your processor for some heavy transcoding or 3D modeling or even gaming (in games that support hyper threading) you will notice significant improvements.

At this point in time Cpu’s that support hyper threading give a 30-50% performance improvement compared to their non-HT CPU counter parts. What the future brings is remained to be seen.


Clock Speed

cpu front and backAfter the name and the number of cores, the first thing you will usually see in a CPU name is the clock speed in Hertz. This tells you the frequency at which the CPU functions. As would be expected, faster is a major advantage in the world of computing, but the relationship of the clock speeds of different CPUs does not directly translate into their performance difference. A good example of this is to look at the Intel Xeon E5-2658 2.1 GHz and the Xeon E3-1280 3.6 GHz. Despite the marked clock speed difference, they both have almost identical benchmark results from PassMark. Primarily, clock speed should be used when looking at models with nearly identical specifications otherwise.

The clock speed is also the main spec of the CPU impacted by overclocking. This allows greater choice in which CPUs are viable for savvy users or those who invest in good heat dissipation systems like water cooling.


CPUs do need to access and store some data in order to perform their function. While the RAM is typically where data is stored for rapid processing, there is still a delay that occurs when transferring information from the RAM to the CPU. For this reason, CPUs are equipped with multiple data stores called caches where the most important bits of data can be stored. You will often see the L3 cache storage amount listed in the tech specs of modern CPUs and sometimes the L2 cache. This is one case where bigger is almost always better, but it is not the most pivotal specification.


Power Draw

The CPU is not the biggest power hog in a gaming rig, but it does contribute a decent percentage of the energy usage. You will find it listed under Thermal Design Power (TDP) when investigating the CPU specs. The TDP is not an indicator of the constant power draw of the CPU, but rather the maximum power it is designed to draw.

Getting more performance generally requires more power consumption, so you will have to make the choice of whether 10 or 20 Watts of TDP is worth the drop in processing power. For gaming PCs, the TDP is more important for understanding the type of cooling apparatus you will need, as a higher power draw means more heat. Under 100W, you should be fine with a heat sink and fan, but once you go above that and begin overclocking, water-cooling becomes the better solution.


Onboard Graphics

A few CPUs, most notably AMD chips, come with graphic processing capability. For people building gaming rigs whether or not your CPU has integrated graphics is inconsequential as it will have no impact once your discrete graphics card is operating. For those just building simple work computers, onboard graphics can provide a decent level of graphical capability while lowering cost and power consumption by forgoing a video card. You will want to look at the performance specs for the integrated graphics and look at its speed to get an idea of its capability.


Cpu Benchmark Testing

processor-benchmark-software-600x323Once you have narrowed down which CPUs you might buy, it is time to start looking at benchmark comparisons. A good benchmark test will try to match the other components as closely as possible, but you can expect some differences in the motherboards. PassMark’s CPU benchmark is one of the most commonly used tests, and other benchmarking tools can be found in our benchmarking guide.
Intel chips are probably your best bet for the highest performance, but at lower levels you should be able to find comparable AMD CPUs. Make sure to match up your CPU socket to the one that is on your motherboard. The clock rate is a decent gauge of the capabilities of a CPU, but only use it as a direct comparison between chips built on the same architecture. The number of cores is not as important today due to programming methodology used by many developers, but you should get at least a quad core to prepare for more developers to take advantage of multi-threading.

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