Desktop Core i3 family spans four generations of processors, Westemere-based Core i3-5xx series, Sandy Bridge-based i3-2xxx, i3-3xxx Ivy Bridge series, and, finally, Haswell i3-4xxx CPUs. Different generations had somewhat different feature sets. Standard features of first Core i3s were 4 MB L3 cache, SSE4 SIMD extensions, and support for Intel 64, Virtualization and Hyper-Threading technologies. Westmere chips used socket 1156 (LGA1156).
The second Core i3 generation added AVX instructions, doubled DMI interface bandwidth, improved graphics performance, and had reduced power consumption. The i3-2xxx processors utilized socket 1155, which was incompatible with the LGA1156. The size of L3 cache on these chips was decreased to 3 MB.
The third Core i3 generation had all of the features of its predecessor, and it further improved GPU performance and TDP. Slightly more efficient Ivy Bridge Core i3s also featured new Float 16 (F16C) instructions, and they had greater memory bandwidth.
The fourth, and the last at the moment, generation of desktop i3 CPUs switched to different socket, called LGA1150, or socket 1150. Powered by Haswell microarchitecture, these microprocessors added AES, AVX2 and FMA3 instructions, tremendously boosted graphics performance, and had a voltage regulator integrated on a chip. Some Haswell Core i3s had the size of L3 cache increased back to 4 MB.
Future Core i3 microprocessors could be based on Skylake 14nm microarchitecture, which is coming to desktop systems in mid-2015. These CPUs will adopt a new socket, called LGA1151.
Regardless of their underlying microarchitecture, all production Core i3 CPUs have 2 cores, and support Hyper-Threading technology, which allows them to run 4 threads at once. The i3 desktop microprocessors have very decent performance, which is close to or exceeds performance of the fastest Core 2 Duo parts. Core i3s are not as fast as Core i5 and i7 CPUs, but they are priced much cheaper, and, consequently, have better price / performance ratio.