Why is it not recommended to install all four memory modules?

If you are currently using an ATX motherboard or an MATX motherboard, it is very likely that the board provides four memory slots. Have you ever wondered how great it would be to fill all four memory slots? In fact, even if the motherboard has four memory slots, I do not recommend filling them all. The reason is simple: performance can actually degrade when all four memory slots are populated.

Consumer-grade processors typically support dual-channel memory, whereas processors designed for commercial use provide support for four or eight channels. Even if all four memory slots are populated, it does not mean four-channel operation; it remains dual-channel. The theoretical speed does not differ significantly from correctly installing two memory modules to form a dual-channel configuration.

Even though both configurations are dual-channel, why does populating four modules perform worse than just two? The reason lies in the memory frequency. When only two modules are installed, the memory can easily run at the rated frequency without issues. However, when all four slots are populated, the situation becomes more complex. Typically, the maximum stable frequency after installing four modules is lower than the rated frequency. For example, DDR5 4800MHz memory will run at 4800MHz with two modules installed, but with four modules, the frequency may drop to 4000MHz to maintain stability.

This naturally impacts actual performance. Taking DDR5 4800MHz memory as an example, when two modules form a dual-channel configuration, measured memory performance is: read speed 74,975 MB/s, write speed 68,123 MB/s, copy speed 67,952 MB/s, and latency 79.6 ns.

When all four DDR5 4800MHz modules are installed, the performance changes to: read speed 62,705 MB/s, write speed 60,898 MB/s, copy speed 61,452 MB/s, and latency 101.4 ns.

The results clearly show that the memory’s read, write, and copy performance all degrade to varying degrees, while latency also increases. This is why it is recommended to install only two memory modules to form a dual channel, as there is no need to fill all four slots.

This situation not only occurs on desktops but also on laptops. Indeed, some flagship gaming laptops provide four memory slots, and when all four are populated, the memory frequency similarly drops.

If filling all memory slots reduces performance, then why do motherboard manufacturers provide four memory slots? Actually, the main purpose of having four memory slots is to allow users to have larger memory capacity. In other words, when the tasks you need to handle prioritize memory capacity over memory frequency, filling all four memory slots makes sense.

For example, creative work, modeling, and similar tasks have very high demands for memory capacity. If the memory capacity is insufficient, the efficiency of running professional software will be greatly reduced, whereas memory frequency does not significantly improve work efficiency. In such cases, filling all four memory slots is perfectly fine.

However, for the vast majority of ordinary users, the main demands are still gaming and daily office work. These demands do not have stringent requirements on memory capacity; instead, the higher the memory frequency, the faster the processing speed. Especially for gaming, memory bandwidth is very important. In this case, naturally, installing two memory sticks to form a dual channel is sufficient.

In summary, for consumer-grade hardware, even if all four memory slots are filled, it still operates in dual-channel mode, so memory bandwidth will not improve. On the contrary, because filling all memory slots places higher demands on motherboard routing and the processor’s memory controller, the memory can only run stably at a lower frequency, which reduces memory performance. For gamers and similar users, memory frequency is more important than memory capacity, so two memory sticks forming dual channel is enough. For creators and other users, memory capacity is more important than memory frequency, so filling all four memory slots is very beneficial.