DDR4 versus DDR5 laptop memory: what fits what

Why the two will never swap

DDR4 and DDR5 laptop modules look almost identical: the same small SODIMM board, roughly 70mm long, with chips on one or both sides. They are not interchangeable. A DDR4 SODIMM has 260 pins and a DDR5 SODIMM has 262, and the locating notch sits in a different place on each, so a module of the wrong generation will not seat in the slot. Nobody damages a machine this way if they stop when the module does not go in, but plenty of time is lost ordering, unpacking and returning memory that was never going to fit.

The electrical design differs too. DDR5 runs at a lower voltage and carries its own power management chip on the module, where DDR4 takes regulated power from the motherboard. Each DDR5 module is also split into two independent 32-bit channels, which is part of why it copes better under heavy load. None of that matters when you are sorting stock, except as a reminder: the motherboard decides which generation a laptop takes, and nothing you fit afterwards changes it.

Which generations take which

For the business laptops that make up most trade lots, the processor generation is the best first guide. Intel's 6th to 11th generation Core processors, from the Skylake machines of 2015 through to Tiger Lake in 2020 and 2021, use DDR4 in the great majority of business models where the memory is socketed. A few 6th and 7th generation machines still took the older DDR3L: Lenovo's ThinkPad T460 is a common example, while the slimmer T460s took DDR4.

Intel's 12th and 13th generation chips are the crossover. The processors support both DDR4 and DDR5, so each laptop maker chose, and the same generation shipped both ways. HP's EliteBook 840 G8, on 11th generation Intel, takes DDR4; the 840 G9 that replaced it, on 12th generation, takes DDR5. Some makers kept DDR4 on their mid-range lines for a while longer to hold costs down. For any 12th or 13th generation model, check the specific model rather than the processor.

From Intel's Core Ultra processors onwards, socketed laptop memory means DDR5, where there are slots at all; many thin models use soldered LPDDR5X instead. On AMD, the Ryzen 5000 series and the later 7030 series use DDR4, while Ryzen 6000, the 7035 and 7040 series and later chips use DDR5 or soldered LPDDR5.

Read the module label

Listings and spreadsheets are a starting point, but the label on the module is the record that counts. Modules from the major memory makers carry a JEDEC speed code. DDR4 modules read PC4 followed by a speed, such as PC4-2666V or PC4-3200AA. DDR5 modules read PC5, such as PC5-4800B or PC5-5600B. If the code starts PC4, the module is DDR4, whatever the listing says.

The same label usually shows the capacity and organisation, written like 16GB 2Rx8, meaning two ranks of chips, each chip eight bits wide. Rank matters little for a laptop upgrade, but matching it across a pair keeps behaviour predictable. A DDR5 module also gives itself away with a small power management chip on the board, separate from the memory chips, which a DDR4 module does not have.

When you cannot see the module, the machine will tell you. The BIOS or UEFI setup screen lists the installed memory and its speed on most business laptops, and in Windows, Task Manager's Performance tab shows the speed, the number of slots used and the form factor. Checking two or three units from a lot before ordering memory for the whole lot is time well spent.

Soldered memory and single slots

The biggest trap is memory that cannot be changed at all. Low-power LPDDR memory is always soldered to the motherboard, and many thin business models use it: what the machine shipped with is what it keeps. A spreadsheet line showing 8GB on such a model is a permanent 8GB, and it should be priced and described that way.

Other models mix the two, with some memory soldered to the board and one free SODIMM slot. On these, a machine with 8GB soldered can take a 16GB module to reach 24GB, but the slot is the only part you can upgrade. Two-slot machines shipped with a single module are common too, and they run in single channel until a second module goes in. Knowing which layout a model uses tells you what an upgrade can achieve before you buy a single module.

Speed, capacity and pairing

Within a generation, speeds are forgiving. A DDR4-3200 module fitted to a laptop rated for DDR4-2666 runs at 2666; a DDR5-5600 module in a machine rated for 4800 runs at 4800. The memory falls back to a speed the system supports, so stocking the faster modules covers several models without trouble. The reverse also works, but a slower module holds the machine below its rated speed.

Two matching modules in a two-slot laptop run in dual channel, which noticeably helps machines that rely on the processor's built-in graphics. A single 16GB module and a pair of 8GB modules give the same capacity, but the pair usually makes the better machine, and resale buyers who check will notice. Mixed sizes work on most modern platforms, with only part of the memory running in dual channel, so match pairs where you can.

Check the maker's stated maximum before fitting large modules. Business laptops of the same generation can list very different ceilings, and going beyond what the specification sheet states may or may not work. It is not something to promise a buyer on the strength of one machine that happened to accept it.

A quick check before you order

Before ordering memory for a lot, confirm four things on a sample unit: the generation, from the module label or the BIOS; how many slots are fitted and how many are free; whether any memory is soldered; and the maximum the model supports. With those answered, ordering is straightforward.

When the modules arrive, keep DDR4 and DDR5 laptop memory in separate, clearly labelled trays. It prevents the most common memory mistake in a busy workshop: a module of the right size and the wrong generation, picked up in a hurry.