DDR4 vs DDR5: what is the difference, and which do you need?

They genuinely do not interchange

DDR4 and DDR5 have the notch in a different place on the module. That is deliberate, so that nobody can force the wrong one in and destroy it — which means buying the wrong kind gives you a stick that will not seat at all, rather than one that seats and runs slowly.

And a motherboard takes one kind only. No board accepts both, not even boards whose names are nearly identical.

What decides it

Start from the CPU you picked and the answer follows.

So if you have chosen an AM5 CPU, this question was settled at that moment and needs no more thought. On Intel LGA1700 you have to read the board listing carefully, because there really is a choice and it really can be got wrong.

How much faster is it, really?

DDR5 has more bandwidth and runs at far higher frequencies, and the numbers on the box differ plainly — the DDR4 people actually buy sits around 3200MHz, while DDR5 starts at 4800MHz and this catalogue goes up to G.Skill Trident Z5 RGB DDR5 32GB (2x16GB) 6400 at 6400MHz.

Bandwidth on paper and speed you can feel are two different things, though. Most of what a home machine does — games, browsing, ordinary editing — is not limited by memory bandwidth, so the gap is usually a few per cent rather than something you could identify blind.

What you can feel is capacity. Going from 16GB to 32GB does more for having many things open at once than any frequency step does — so if you can only afford one, buy capacity before speed.

The short version

• Building new this year, DDR5 is the default — and with an AM5 CPU there is no alternative anyway.
• DDR4 still makes sense in exactly one case: you already own DDR4 and want to keep using it, which means choosing an LGA1700 board in its DDR4 version.
• Never pick a board on its model name alone. Read the memory-type field every time before you order.
• Capacity beats frequency. For most people 32GB at 5200MHz is the better machine than 16GB at 6400MHz.