What's the difference between an Intel Core i3, i5 and i7?

Intel Core i3, Core i5, and Core i7 CPUs have been around for over a year now, but some buyers still get stumped whenever they attempt to build their own systems and are forced to choose among the three. With the more recent Sandy Bridge architecture now on store shelves, we expect the latest wave of buyers to ask the same kind of questions.

Core i3, Core i5, Core i7 — the difference in a nutshell

If you want a plain and simple answer, then generally speaking, Core i7s are better than Core i5s, which are in turn better than Core i3s. Nope, Core i7 does not have seven cores nor does Core i3 have three cores. The numbers are simply indicative of their relative processing powers.

Image credit: Intel.

Their relative levels of processing power are also signified by their Intel Processor Star Ratings, which are based on a collection of criteria involving their number of cores, clockspeed (in GHz), size of cache, as well as some new Intel technologies like Turbo Boost and Hyper-Threading.

Core i3s are rated with three stars, i5s have four stars, and i7s have five. If you’re wondering why the ratings start with three, well they actually don’t. The entry-level Intel CPUs — Celeron and Pentium — get one and two stars respectively.

Note: Core processors can be grouped in terms of their target devices, i.e., those for laptops and those for desktops. Each has its own specific characteristics/specs. To avoid confusion, we’ll focus on the desktop variants. Note also that we’ll be focusing on the 2nd Generation (Sandy Bridge) Core CPUs.

Number of cores

The more cores there are, the more tasks (known as threads) can be served at the same time. The lowest number of cores can be found in Core i3 CPUs, i.e., which have only two cores. Currently, all Core i3s are dual-core processors.

Currently all Core i5 processors, except for the i5-661, are quad cores in Australia. The Core i5-661 is only a dual-core processor with a clockspeed of 3.33 GHz. Remember that all Core i3s are also dual cores. Furthermore, the i3-560 is also 3.33GHz, yet a lot cheaper. Sounds like it might be a better buy than the i5. What gives?

At this point, I’d like to grab the opportunity to illustrate how a number of factors affect the overall processing power of a CPU and determine whether it should be considered an i3, an i5, or an i7.

Even if the i5-661 normally runs at the same clockspeed as Core i3-560, and even if they all have the same number of cores, the i5-661 benefits from a technology known as Turbo Boost.

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