The 4x8GB of DDR4-3200 memory in use here at Harcore Games is modest but for gaming it is already far ahead of the curve. The G.Skill Flare X RAM is composed of 4 gigabit chips spanning both sides of the DIMM. DDR4 tops out at 4x16GB with standard 8 gigabit chips. Larger capacity DDR4 DIMMs are using dual rows of chips which is unorthodox and not widely supported.
Most recently however there has manufacturing of 16 gigabit chips which are now being made into 32GB DIMMs for richer consumers. The X570 is capable of recognizing 32GB memory which represents the maximum 128GB.
When DDR5 hits the market with 8, 16 and 32 gigabit chips. Speeds will range from DDR5-4800 to DDR5-6400. The larger 16 gigabit chips will make it possible to install 4x32GB. The largest 32 gigabit chips will allow 4x64GB which is more than mainframe supercomputers had 15-20 years ago.
RAM price erosion made the 32GB installed very affordable and eventually 64GB will become more affordable. The move to 64GB can be pondered depending on the cost and whether it is really necessary. The existing RAM is expected to be in use for several years as the X570 platform is intended to be in long term use.
The cost for 128GB on the desktop gaming PC may be possible in 3-4 years based on historical price erosion. DDR5 is expected to span foundry capability down to 7nm or smaller. The idea of 256GB of RAM is mind boggling but maybe in 5 years it may be possible.
First of all, the die size is set at 76.22 square mm, so it is towards the higher end of historical DRAM die sizes. For 16 gigabit chips, this means that the manufacturing prices will be quite high, but the 8 gigabit version should be more cost effective than the current DDR4 chips. The structure of the 16 gigabit chip includes 32 banks or 8 bank groups of 4 banks each.
When DDR5 is launched the price premium is the reason the X570 will be in service for a longer time period. It may take 2 or 3 years or more for price erosion to make even 4x8GB as affordable as the DDR4-3200 was recently procured.
Samsung is making LPDDR5 for mobile devices already. SK Hynix is gearing up DDR5 while Micron is making DDR5 memory for corporate servers. DDR5 should largely replace DDR4 in servers over the next 4-5 years.
Neither AMD or Intel have yet announced any intentions for DDR5 for gaming platforms. When they do move forward, the migration to DDR5 will be slower than the corporate overhaul. Price erosion will eventually make DDR5 more desirable for consumers.
Servers will be the first to adopt DDR5 primary as they need more memory for hosting larger numbers of virtual machines. DDR4 capacity is still quite adequate for consumers for a couple of years to come. Intel is more likely to offer consumer hardware based on DDR5 before AMD but neither is likely to anything in 2020.