All of the computers we offer have a minimum of 8GB of memory which provides ample performance for everyday home/office use and general gaming. A popular upgrade is to 16GB which provides some headroom for more demanding applications and games as well as the ability to have more applications running concurrently without performance degradation. 16GB is a low cost upgrade that suits more demanding users. Upgrades to 32 or 64GB are typically only required for specific applications and un-necessary for most users.
When it comes to memory upgrade options you may see reference to 8GB as 4x2GB or 2x4GB, 16GB as 4x4GB or 2x8GB, 32GB ax 4x8GB or 2x16GB. This is because memory is best installed in matching pairs and there are 4 slots on most systems in which we can install memory. The difference between 4x4 and 2x8 is that the 2x8 uses 2 slots and has 2 slots spare for future upgrades (assuming you'd ever need to go above 16GB!) and the 4x4 has all slots full.
All of the 2nd to 4th generation i5/i7 computers use DDR3 ram. While the 6thgeneration and later support the newer/faster DDR4 ram the performance difference is minimal. DDR3 ram is cheaper for us to buy, which means you can get more for less – with more memory capacity often giving better performance than later memory types. When you also consider that the processor benchmarks performed between say an i5-2nd generation and an i5 7th generation that have less than 20% performance variation and then take into account the fact that BOTH the processor is later generation AND the memory is the later DDR4 with both elements contributing to the speed improvement of later generations, it is really isn’t as significant as you might think. Typically you can get better bang for buck spending this money on the graphics or storage options in your computer... it's unlikely that DDR3 would be a bottleneck in any but the most demanding of applications.