DDR4 and DDR5 are not interchangeable, and the choice is usually made for you by the platform rather than being a decision you get to weigh up.
In short
- They are physically keyed differently. A board takes one or the other, never both.
- AM5 is DDR5 only. AM4 is DDR4 only. LGA1700 boards come in both varieties.
- DDR5 has higher bandwidth and higher latency in nanoseconds; the net effect varies by workload.
- Check the board model carefully: DDR4 and DDR5 variants often have nearly identical names.
They do not physically interchange
The notch in the module sits in a different position for each generation, so a DDR4 module cannot be forced into a DDR5 slot or the reverse. This is deliberate, because the electrical signalling and voltage regulation differ, and a module in the wrong slot would be damaged.
A motherboard is built for one generation. There is no board that accepts both, and no adapter.
What DDR5 changed
DDR5 runs at substantially higher transfer rates, splits each module into two independent 32-bit channels rather than one 64-bit channel, and moves voltage regulation onto the module itself.
It also has higher latency measured in clock cycles, and the higher clock speed does not entirely cancel that out in absolute time. So DDR5 moves more data per second but takes slightly longer to deliver the first piece of it.
Which of those matters depends on the workload. Tasks moving large amounts of data benefit from the bandwidth. Tasks dominated by unpredictable access patterns, which includes many games, are more sensitive to latency and see less benefit.
What this means in practice
If you are buying AM5, you are buying DDR5. If you are buying AM4, you are buying DDR4. Neither is a decision.
On LGA1700 you choose, and the honest answer is that DDR4 is the sensible option if you already own it or the price difference is meaningful, while DDR5 makes sense on a new build with no existing memory. The performance gap is small enough that it should not drive the decision on its own.
Where the difference does show up
Two situations where DDR5 is clearly worth having rather than marginally better.
Integrated graphics. These share system memory and are limited by bandwidth more than by anything else, so the extra throughput translates directly into graphics performance. A machine relying on integrated graphics benefits substantially.
Memory-heavy productivity work. Large file operations, video timelines and simulation move enough data for bandwidth to matter.
Where it shows up least is gaming with a dedicated graphics card, which is what most people are actually asking about. There the difference is usually a few percent, and frequently less than the difference between a well-tuned DDR4 kit and a poorly configured DDR5 one.
On-module voltage regulation
One structural change worth knowing about. DDR4 modules are fed regulated voltage from the motherboard; DDR5 modules carry their own regulation on the module itself.
The practical effect is that module quality matters more than it did, since the regulation circuitry is part of what you are buying rather than part of the board. It is one reason cheap DDR5 kits vary more in overclocking behaviour than cheap DDR4 ones did.
It also means DDR5 modules run slightly warmer, which is why heat spreaders became standard rather than decorative on this generation.
Board manufacturers frequently sell DDR4 and DDR5 versions of the same model with almost identical names, distinguished only by a D4 or D5 suffix. Check this carefully at the point of ordering. It is a common and expensive mistake, and the PC Builder catches it if you select both parts.