Difference Between Core i3, Core i5 Core i7

The difference between core i-series (i3, i5 and i7) is define as :
The numbers after the letter "i" are a high level indicative of the processors' relative processing power.
i3 - less power... i7 - more power. Processing power is determined by their Intel Processor Star Ratings, which is 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. About cores: Simply, 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.
Turbo Boost Technology allows a processor to dynamically increase its clockspeed whenever the need arises. Cache is just like RAM, only faster —
because it’s built into the CPU itself. Both RAM and cache serve as holding areas for frequently used data. Without them, the CPU would have to keep on reading from the hard disk drive, which would take a lot more time. Hyper-Threading enables a single core to serve multiple threads. A Core i3, which is only a dual core, can actually serve two threads per core. In other words, a total of four threads can run simultaneously. Core i7 are quad cores, plus they also support Hyper-Threading. giving them a total of eight threads that can run on them at the same time. Combine that with 8 MB of cache and Intel Turbo Boost Technology, which all of them have, and you’ll see what sets the Core i7 apart.
These are the configuration of core i-series :

-> Core i3:

* 4 Threads
* Entry level processor.
* 2-4 Cores
* Hyper-Threading (efficient use of processor
resources)
* 3-4 MB Cache
* 32 nm Silicon (less heat and energy)

-> Core i5:

* 4 Threads
* Mid range processor.
* 2-4 Cores
* Turbo Mode (turn off core if not used)
* Hyper-Threading (efficient use of processor
resources)
* 3-8 MB Cache
* 32-45 nm Silicon (less heat and energy)

-> Core i7:

* 8 Threads
* High end processor.
* 4 Cores
* Turbo Mode (turn off core if not used)
* Hyper-Threading (efficient use of processor
resources)
* 4-8 MB Cache
* 32-45 nm Silicon (less heat and energy)