Searching for Intel i3-6100 will bring up the Intel Product Specifications page for this processor. It is a 6th Generation two core processor with Hyper-Threading support to give four threads, and has an integrated graphics unit. Dating from late 2015 one of its features is that it supports either DDR3 or DDR4 memory. And the i in i3 stands for - who knows, probably just a marketing thing. The i3, i5, i7 and i9 designations were a way of indicating the relative power (and cost) of Intel's range of processors. The i3 CPUs were generally the least expensive, and had less in terms of cores, cache, chip speeds etc. But they were capable and good value for money.
The i3 etc designation is not being used after the 14th Generation. Instead there is Intel Core 3, Core 5 and so on. To this may be added Ultra which signifies a number of features, the main one of which is the presence of a Neural Processing Unit (NPU).
