RAM – DDR4 vs DDR5, capacity, channels and speed
The difference between DDR4 and DDR5, why they are not interchangeable, what MT/s means, dual-channel mode, and why four modules can run slower than two.
The short version
- DDR4 and DDR5 are not interchangeable. The memory type is set by the motherboard, not just the processor.
- Speed is given in MT/s (millions of transfers per second). A figure such as "up to DDR5-5600" applies under the conditions the processor maker states – e.g. the number of modules.
- Two modules in the right slots enable dual-channel mode. On mainstream platforms, four modules often mean a lower maximum speed.
DDR4 and DDR5 cannot be mixed
Desktop DDR4 and DDR5 modules both have 288 contacts, but the notch is in a different place. A slot on the board is designed for one type – the other will not physically go in. DDR5 also moved voltage regulation (the PMIC) onto the module itself.
The memory type is set by the board. On AMD AM5 and Intel LGA1851 it is always DDR5. On the older Intel LGA1700 platform the processor supports both types (for the Core i9-14900K, Intel lists DDR5 up to 5600 MT/s and DDR4 up to 3200 MT/s), but a board only has slots for one of them.
What the speed means
Memory speed is given as the number of transfers per second, MT/s. Processor makers state which speed they guarantee. For the Ryzen 9 9950X, AMD lists:
| Configuration | Max. speed (AMD) |
|---|---|
| 2 modules, single-rank (2×1R) | DDR5-5600 |
| 2 modules, dual-rank (2×2R) | DDR5-5600 |
| 4 modules, single-rank (4×1R) | DDR5-3600 |
| 4 modules, dual-rank (4×2R) | DDR5-3600 |
The table has a practical consequence: if you need a lot of memory, it is better to buy two larger modules than four smaller ones. Four modules on a dual-channel platform put more load on the memory controller, and the guaranteed speed drops.
EXPO (AMD) and XMP (Intel) profiles on the module set a higher speed than the processor maker guarantees. AMD notes that operating outside published specifications is overclocking. It usually works, but stability is not guaranteed.
Dual-channel mode
Mainstream desktop processors have two memory channels (both AMD and Intel list “Max # of Memory Channels: 2” for the processors mentioned). With a single module you use one channel and half the available bandwidth. That is why two identical modules are recommended, in the slots specified in the board manual.
How much memory
Recommendations by use change as software changes, so we do not give a “correct” number here. It is more useful to look at how much memory you actually use: in Windows in Task Manager (Performance tab → Memory), on macOS in Activity Monitor. If usage stays close to the maximum and the system is writing to the page file, more RAM will help. If a third is free, more memory will not make things faster.
For comparison, Microsoft lists 4 GB of RAM as the minimum for Windows 11, and 16 GB of DDR5/LPDDR5 for Copilot+ PCs. A minimum, however, is not a comfortable amount for everyday work.
Laptops: SO-DIMM or soldered memory
Laptops use shorter SO-DIMM modules or have the memory soldered directly onto the board (often labelled LPDDR). Soldered memory cannot be upgraded. If you plan to use a laptop for many years, find out before you buy – in the maker’s technical specification or service manual.
Before you finish
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Notes and sources
- AMD: AMD Ryzen 9 9950X – specifications (TDP 170 W, AM5, DDR5)
- AMD: AMD Ryzen 7 9700X – specifications (TDP 65 W, AM5, DDR5)
- Intel: Intel Core Ultra 9 285K – specifications (FCLGA1851, DDR5, PBP 125 W / MTP 250 W)
- Intel: Intel Core i9-14900K – specifications (FCLGA1700, DDR5 and DDR4, MTP 253 W)
- AMD: AMD Socket AM5 Chipset – chipsets, PCIe lanes, USB
We opened every link above and compared the figures on 12 October 2026. The pages belong to their publishers and can change after that date.
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