RAM Compatibility: How to Check What Fits Your PC

Your motherboard decides what fits

RAM compatibility starts with the motherboard. It fixes the memory generation (DDR4 or DDR5), the number of slots and the maximum capacity. Kingston puts it plainly: DDR4 and DDR5 are not interchangeable, and the board, never the processor alone, tells you which one to buy.

The processor still sets limits. Intel Core 12th to 14th gen chips handle both types: Intel lists the Core i5-14600K with up to DDR5 5600 or DDR4 3200, depending on the board it sits in. AMD AM5 and Intel Core Ultra 200S take DDR5 only, while a Ryzen 5000 on AM4 is a DDR4 platform. If these terms are new, our guide to what RAM is covers the basics first.

What RAM do I have?

Before you buy, find out what is already installed. On Windows 11, Settings, then System, then About shows the installed RAM under Device specifications. Task Manager (Ctrl+Shift+Esc), on the Performance tab under Memory, adds the speed, the form factor and how many slots are in use.

Windows does not show whether the memory is DDR4 or DDR5 in those screens. How-To Geek gives a workaround: open PowerShell and run Get-CimInstance win32_physicalmemory. The MemoryType field reads 26 for DDR4 and 27 for DDR5. If it shows 0, look up the part number the same command lists, along with the maker, capacity and slot of each module. Menus can differ slightly between Windows builds.

Write down what you find: type, number of sticks, capacity per stick, speed and brand. Corsair's upgrade checklist asks for exactly that, plus the motherboard model, the CPU, the maximum memory the pair supports and whether any slots are free. On a desktop, also check the height under a large CPU air cooler, because a tall module can block it.

Using a RAM compatibility checker

A RAM compatibility checker matches your system to modules that are known to work in it. There are three places to look, and they work best together.

1. The motherboard maker's specification page. Search the exact model. It lists the memory type, slot count, maximum capacity and supported speeds, and that is the line that settles the question.
2. A memory maker's configurator. Kingston recommends entering your motherboard or system model in its Memory Configurator to confirm which modules are validated. Kingston adds that the Configurator also shows the maximum memory a system can use.
3. The kit's QVL. G.Skill offers a RAM Configurator and publishes a QVL, a list of motherboards each kit was tested with, on its product pages. If your board is on the QVL of the kit you want, that is the safest answer you can get.

For a prebuilt PC or a laptop, enter the system model rather than the motherboard, since Kingston's Configurator takes either.

Can you mix DDR4 and DDR5 RAM?

No. Kingston says DDR4 and DDR5 cannot be mixed on the same motherboard: they have different pin layouts, voltages and signalling, and the notch sits in a different place, so a DDR5 module will not go into a DDR4 slot. DDR4 runs at 1.2V and DDR5 at 1.1V, and DDR5 moves the power management chip onto the module itself.

That also means moving from DDR4 to DDR5 is never just a memory swap. Kingston notes it needs a compatible motherboard and processor as well. On Intel LGA 1700 (12th to 14th gen Core), both board types exist, so check which one you have. LGA 1851 (Core Ultra 200S, 800 series boards) dropped DDR4.

The table shows which memory each common platform takes, with the cheapest 32GB desktop kit we found at Amazon.co.uk, AWD-IT, Box, CCL, Laptops Direct, Overclockers UK and Scan this week, prices including VAT.

For a fuller look at the two generations, see DDR5 vs DDR4. Every kit and its price is on our DDR5 RAM prices and DDR4 RAM prices pages.

Dual channel, four sticks and 64GB

Fitting in the slot is one thing; running at the speed on the box is another. Mainstream desktop platforms are dual channel. Kingston explains that dual channel bandwidth needs an identical pair of modules, and that AMD and Intel DDR5 platforms limit memory speed when all four slots are filled. Two larger modules are the better choice over four smaller ones.

AMD's own figures for the Ryzen 9 9950X show the gap: DDR5-5600 with two modules, DDR5-3600 with four. So for dual channel 64GB RAM, buy a 2 x 32GB kit rather than four 16GB sticks. Kingston lists 32GB as the largest DDR4 desktop module and 64GB for DDR5, which matters if you plan to grow beyond 64GB later.

To buy compatible RAM with the least risk, get a matched kit. Corsair says replacing all modules with one kit is the only way to guarantee the modules work together, because kits are tested as a set. Adding a second kit costs less, but can cause trouble, especially above the speed the CPU maker certifies. If you add one anyway, match the type, capacity and speed of what is installed.

Your new kit will usually start below its rated speed. Without XMP (Intel) or EXPO (AMD) switched on in the BIOS, a DDR5-6000 kit typically runs at a JEDEC default of 4800 or 5600 MT/s. Both makers class these profiles as overclocking, outside their official spec.

The table shows the cheapest 64GB desktop kits we found this week. Our 64GB RAM prices page lists them all.

How to buy compatible RAM for a laptop

Laptops use SO-DIMM modules, smaller than the DIMMs in a desktop, and the two are not interchangeable. Micron's datasheets give 262 pins for a DDR5 SO-DIMM and 288 for a desktop DDR5 UDIMM. Start with the laptop's spec sheet: it tells you whether the memory can be replaced, how many slots there are and the supported maximum.

Corsair warns that some laptops have memory soldered to the board, which cannot be upgraded, and that going over the supported maximum can stop the laptop booting. With a free slot, match the type, capacity and speed of the module already fitted. Apple silicon Macs are fixed too: Apple says the memory is part of the chip package and you choose it when you buy.

Before you open the case, Kingston advises shutting the machine down, unplugging the power adapter and touching bare metal to discharge static; a wrist strap is better. Laptop module prices are on our laptop RAM page, and our RAM upgrade guide walks through fitting them.

Common mistakes

• Choosing by processor alone. An Intel Core 12th to 14th gen chip can sit on a DDR4 or a DDR5 board. Only the board decides.
• Trusting the speed on the box. Without XMP or EXPO, the kit runs at its standard speed.
• Filling four slots when two will do. AMD's guaranteed speed drops with four modules.
• Mixing two kits. Kits never tested together do not always hold their rated speed.
• Forgetting the cooler. A tall module can clash with a large air cooler.
• Mixing up formats. A SO-DIMM does not fit a desktop slot, and Kingston notes that a DDR5 server RDIMM does not fit a board built for unbuffered modules. Our ECC RAM guide explains the difference.
• Guessing the slot order. It changes per board, so follow the manual. Our guide on how much RAM you need helps you pick the size first.