Overclocking will void the warranty of your retail CPU. Overclocking may destroy your CPU, your motherboard, or your system memory. It may corrupt your hard drive. Be careful when overclocking. You have been warned.
After reading this disclaimer, you may be inclined to walk away. Don't. Moderate overclocking is mostly safe.
These days, Intel and AMD don't frown on overclocking as much as they did a few years ago. Both companies now ship CPUs equipped with core multipliers (which we'll discuss shortly) unlocked, and even CPUs that have locked multipliers are fairly easy to overclock.
First, though, let's take a look at a few overclocking myths.
Myth #1: Overclocking requires expensive liquid cooling or very noisy air coolers.
Actually this isn't a myth if you're planning on doing extreme overclocking. But moderate overclocking (one to two speed grades higher than spec) is often achievable without replacing or supplementing the stock cooler supplied with a retail CPU. On the other hand, a better cooler can extend the life of the product at those higher clock speeds.
Myth #2: Different iterations of the same chip have the same capacity for overclocking.
Because the manufacturing yield is a statistical distribution, you'll probably get a CPU that can run much faster the listed speed, but you might end up with a processor that runs only about 10% faster. Consequently, the fact that your buddy down the street can run a Core i5 750 (rated at 2.66GHz) at 4GHz doesn't mean that your Core i5 750 CPU can will be able to run that fast. That caveat is well worth keeping in mind when you attempt to overclock.
Myth #3: Overclocking requires expensive motherboards and memory.
Not necessarily. We'll look at examples involving a fairly high-end motherboard (roughly $250), a $190 board, and a micro-ATX board that's priced around $140. The $300+ motherboards that gave rise to this myth are luxuries for people bent on extreme overclocking (which requires certain special features). Likewise, unless you want to overclock your DRAM to extreme speeds, modestly priced DRAM (which we'll be using in our examples) will work fine.
We won't dive deeply into individual CPU architectures, but you do need to know some basic stuff.
All CPUs have a fundamental clock rate, from which all of the other clock rates inside the CPU are derived. Various sections of the processor take this fundamental clock rate, which acts as a kind of standard timekeeper, and multiply it to get an internal clock speed for a particular section of the CPU. In the Intel Core i5/i7 series of CPUs, the fundamental clock rate is called the base clock or BCLK (it's usually 133MHz). For its part, AMD calls this rate the CPU bus frequency; it's commonly set at 200MHz in AMD desktop processors.