Intel's Core i3 and i5 processors are among the newest from the company. i3 is low-end (like Core 2), i5 is mid-level and i7 is high-end (like Xeon).
Both Core i3 and Core i5 are based on the Nehalem microarchitecture, which includes an integrated DDR3 memory controller as well as QuickPath Interconnect or PCI Express. The Front Side Bus used in all earlier Core processors has been replaced with Direct Media Interface. The processors have 256 KB L2 cache per core, plus up to 12 MB shared Level 3 cache.
edit Architecture and Specifications
The first Core i3 processor was launched on January 7, 2010. It was Clarkdale-based, (desktop) with an integrated GPU (Graphics Processing Unit) and two cores.
Intel Core i5 was launched on September 8, 2009. The first such processor was Core i5 750, a quad-core Lynnfield Desktop processor. Later, dual-core mobile processors based on Arrandale microarchitecture were released, followed by Clarkdale-based Core i5-6xx processors. These i5-6xx processors are very similar to cheaper Core i3 processors, with Turbo Boost being the main feature that is missing in the i3.
|Processor||L3 Cache||Socket||TDP||I/O Bus|
|Clarkdale||Core i3-5xx||4 MB||LGA 1156||73 W||Direct Media Interface,|
|Arrandale||Core i3-3xxM||3 MB||µPGA-989||35 W|
|Lynnfield||Core i5-7xx||8 MB||LGA 1156||95 W||Direct Media Interface|
|Core i5-7xxS||82 W|
|Clarkdale||Core i5-6xx||4 MB||73–87 W||Direct Media Interface,|
|Arrandale||Core i5-5xxM||3 MB||µPGA-989||35 W|
|Core i5-5xxUM||18 W|
edit Turbo boost
Turbo boost is the technology that automatically speeds up the processor when the PC needs extra performance. This is done by "dynamic overclocking" i.e. increasing CPU clock-speed. This technology is available in Core i5 processors and does not exist in any of the i3 processors.
edit HD graphics and Hyperthread technology
Hyperthread technology is a four-way multi-task processing that allows each core of the processor to work on two tasks at the same time. HD (High Density) Graphics and Hyperthread technology is available in both i3 and i5 processors except Core i5 750.
Here are some videos that explain the differences between i3 and i5 processors.