CPU Buying Guide

Computers are meant to reduce the complexity in our lives. However, if you're looking to upgrade your current PC or buy an entirely new system, you can quickly become confused by the terminology, especially when it comes to the CPU -- the heart of any computer system. This buying guide will take you through everything you need to know to make an informed CPU buying choice.

These days, it's not just a matter of deciding to buy a particular CPU at a particular price point. You've got to take into consideration the motherboard types that an individual CPU will work with, the additional capabilities that you're looking for in a processor, and the types of software you're likely to run on your machine. It's much better to make the right choice and get a PC that's ideal for your chosen applications than end up with something that sounds good on paper, but can't run the core tasks you need.


What is a CPU?

CPU stands for Central Processing Unit, and even after many years of refinements in PC technology, the CPU is still the core of your computer's operations. It controls the flow of data throughout your entire PC (hence the central part). The processing part is equally vital, as the role of the CPU is to manipulate -- or process -- the data that passes through your computer, reading it from storage devices, changing it as required, and then writing it out to storage or display devices.

At a physical level, a CPU is comprised of millions of microscopic transistors which are etched onto a layer of silicon via chemical and lithographic processes. Transistors themselves are exceptionally simple devices that store binary (on/off) values, and it's from these on/off states that more complicated processes can be performed. To give you an idea of the complexity of a modern transistor, a dual-core CPU such as Intel's Core 2 Duo E6700 is comprised of just under 291 million transistors. For a quad-core chip like Intel's Core 2 Extreme QX6850, that transistor count jumps to around 582 million.

In order to perform any useful data task, a CPU needs a few basic components. While the exact detail of how each processor does this varies quite widely depending on the architecture of that particular model, the basics remain the same. A CPU needs to be able to get data in, transform it meaningfully, based on the instructions it is given, and then send that data to a suitable repository. The repository might be a storage medium like a hard drive, a visual display like a monitor, or even the CPU itself for further calculations.

At the simplest level, the CPU needs only four elements to perform its data operations: instructions, an instruction pointer, some registers, and the arithmetic logic unit.

The instruction pointer tells the CPU where in memory the instruction it needs to run is located.

Registers are temporary storage locations on the CPU. A register holds data waiting to be processed by an instruction, or data that has already been processed (say, the result of adding two numbers together).

The arithmetic logic unit, or ALU, acts as the CPU's calculator, performing the maths and logic functions dictated by the instructions.

As well as these core elements, the CPU has some additional parts that help those core elements do their jobs:

  • The instruction fetch grabs instructions from RAM or an area of memory located on the CPU;
  • The instruction decoder takes the instruction from the fetch and translates it so the CPU understands. It then determines what steps are necessary to accomplish that instruction;
  • The control unit manages and coordinates all the operations of the chip. It lets the ALU know when to calculate, tells the fetch when to grab a value, and tells the decoder when to translate the value into an instruction.

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