What is RAM? Types, speeds and how much you need

What does RAM do?

RAM (random access memory) is the working memory of a computer. When you open a program, a browser tab or a game, the processor loads the data it needs from the SSD into RAM, because RAM is many times faster to read and write. The processor then works from RAM, not from the SSD.

RAM is volatile, so everything in it disappears when the power goes off. That is why your files live on the SSD and only the things you are using sit in RAM. When RAM fills up, the system starts pushing data back to the much slower SSD. You notice that as stutter, slow tab switching and long waits after you switch between windows.

RAM or storage?

People mix the two up because both are counted in gigabytes. A typical PC in 2026 has 16GB or 32GB of RAM and 1TB or 2TB of storage. More storage lets you keep more files and games installed. More RAM lets you keep more of them open at once without slowdown.

Buying more RAM does not free disk space, and a bigger SSD does not cure a PC that runs out of memory. Find out which of the two is the problem before you spend: on Windows, Task Manager (Performance tab) shows memory use as it happens.

DDR3, DDR4 and DDR5

Memory comes in generations, and each only fits its own motherboards. DDR5 runs at 1.1 volts against 1.2 volts for DDR4, and the notch in the module is in a different place, so a DDR5 stick will not go into a DDR4 slot. DDR5 also starts at 4800 MT/s, where official DDR4 speeds end at 3200 MT/s. It carries its own power management chip on the module too.

You can tell the generation from the label. PC5-48000 is DDR5 and PC4-25600 is DDR4. DDR3 only matters if you are keeping a very old PC alive, and UK shops stock very little of it.

The table shows the two current generations with the cheapest desktop kits we found in UK shops this week.

Prices include VAT. Current AMD AM5 and Intel Core Ultra 200S desktop platforms only take DDR5. DDR4 is for the many systems from roughly 2016 to 2022 that still run it.

Speed and latency in plain English

Two numbers on the label tell you how quick a kit is. The speed, in MT/s (often written MHz), is how many transfers per second the memory makes. The CAS latency, CL, is how many clock cycles the memory waits before it answers. Higher speed is better and lower CL is better, and they pull against each other.

To compare fairly, work out the true latency in nanoseconds: CL times 2000, divided by the speed in MT/s. DDR5 6000 CL30 comes to 10 ns, and so does DDR4 3200 CL16. That is why a DDR5 kit with a bigger CL number is not slower to respond. At the same latency, the faster kit has more bandwidth.

For AMD Ryzen 7000 and 9000, DDR5 6000 CL30 is the commonly recommended kit. It is above AMD's guaranteed speed, so it relies on the EXPO profile, and Intel's equivalent is XMP. A new kit usually starts at a slow default speed until you enable the profile in the BIOS.

How much RAM do you need?

Microsoft lists 4GB as the minimum for Windows 11, but that is a floor, not a recommendation. Newegg's 2026 guide gives rough tiers. 16GB suits browsing, office work, study and most 1080p gaming. 32GB suits gaming with a browser and chat open, photo editing, light video work and the odd virtual machine. 64GB suits serious video editing, 3D rendering, large datasets and local AI models.

The most common amount in the wild is moving up: Valve's September 2026 survey shows 32GB as the most common amount among Steam users, at 42.22%. If you are weighing the step, compare the prices on our 16GB and 32GB pages. This week the median 32GB DDR5 desktop kit costs £499.99 and the median 16GB DDR5 kit £260.99.

If you are unsure whether more memory will help, watch the memory graph in Task Manager during your normal work. If it stays above roughly 85% most of the time, more RAM will help. If it stays well below, a faster SSD or processor will make a bigger difference.

Desktop, laptop and Mac memory

On a desktop, buy memory as a kit of two modules: 2x8GB for 16GB, 2x16GB for 32GB. Two modules run in dual channel and give the processor more bandwidth than one. Our DDR5 price page lists every desktop kit.

Laptops use a shorter module called SO-DIMM. It does the same job but fits only laptop slots, and plenty of thin laptops solder the memory to the board so it cannot be upgraded at all. Check the spec sheet for your exact model before you order. Laptop modules have their own prices, shown on our laptop RAM page.

Macs with Apple silicon are fixed. Apple states that the memory is part of the chip package and cannot be upgraded, so you choose the amount when you buy.

Common mistakes

• Buying the wrong generation. DDR4 and DDR5 look alike in photos. Check the motherboard first.
• Mixing two different kits. Kits that were not tested together can refuse to run at their rated speed, or at all.
• Forgetting XMP or EXPO. Without the profile, a fast kit runs at its slow default.
• Paying for speed you will not notice. Moving from 6000 to 7200 MT/s costs more than it gives in most games. Capacity matters more once you run out.
• Upgrading a laptop with soldered memory. Some models have no free slot at all.