Expansion cards don't usually get tons of attention, but they are some of the most valuable and affordable upgrades you can make to your PC. Instead of buying a new motherboard to get features or ports absent on your existing one, you can often achieve the same result with an expansion card. Your motherboard offers primarily two types of ports for adding an expansion card: PCIe and M.2. While both use the same PCIe bus to communicate with the system, PCIe ports offer practical advantages over M.2 ports. They're way more versatile, offer higher bandwidth and power delivery for serious upgrades, and are also easier to cool. If your motherboard has a few unused PCIe slots, it's always recommended to use them before M.2 slots for expanding your PC's capabilities.

PCIe slots offer potentially higher bandwidth

Even though M.2 uses the same bus

Although the M.2 slot uses the same PCIe connection to the system as PCIe slots, it's typically limited to 4 PCIe lanes. While PCIe 4.0 x4 and PCIe 5.0 x4 configurations are sufficient for SSDs, you may want to use higher-bandwidth configurations for your high-performance expansion cards. This is where PCIe slots prove to be better. Even if you have a discrete GPU in the primary PCIe slot, the secondary slot offers up to eight PCIe 4.0 lanes. When you need to install a second graphics card, a multi-SSD NVMe adapter, or an HBA card, the PCIe 4.0 x8 configuration comes in handy.

You're basically looking at a 128 Gbps connection on PCIe 4.0 x8 vs. 64 Gbps on PCIe 4.0 x4. You'll most likely need to use PCIe bifurcation to borrow 8 lanes from the primary PCIe slot, but that shouldn't affect the performance too much. The M.2 slot is perfect for Wi-Fi cards, USB cards, and SATA cards, but the PCIe slot is recommended when you need all the bandwidth you can get.

Your expansion cards can access way more power

PCIe slots offer way more watts

When it comes to powering high-bandwidth devices, you also need sufficient power to be delivered from the slot in question. The M.2 slot can provide 5-10W of power, whereas a smaller PCIe x8 slot is rated for up to 25W. When you need a multi-SSD NVMe card on your PC, you need to supply around 20–40W of power, depending on whether it's a dual-SSD or quad-SSD card. Your secondary PCIe slot, which may only have access to 8 lanes, is physically an x16 slot and can deliver up to 75W of power, more than enough to support high-performance expansion cards. It can even run a graphics card if its TDP is 75W or lower. Due to the higher power delivery, PCIe slots can support more devices compared to M.2 slots, making them more versatile.

PCIe cards are easier to cool

Better orientation and larger surface area

Cooling efficiency depends on the position of the expansion card and the surface area available for cooling. When you're installing a tiny M.2 card that's powering high-speed Wi-Fi, there's always a chance of running into thermal throttling. M.2 cards located in a cramped case or blocked by a large graphics card can be starved of airflow, which can cause overheating and performance slowdown. PCIe cards, on the other hand, are significantly bigger by design, and can be cooled much more efficiently. In addition to higher bandwidth and power delivery, this advantage makes PCIe slots ideal for high-performance expansion cards. You don't need to be as careful when installing a PCIe card, since the horizontal orientation lends itself to better cooling.

The next time you need serious expansion, trust PCIe over M.2

If you're a power user, you already know that PCIe expansion cards are way better than M.2 options. You have a greater variety to choose from while enjoying higher bandwidth and power delivery. It's also easier to cool a large PCIe card compared to a small M.2 one. Users inexperienced with expansion cards and debating between PCIe and M.2 models should lean toward PCIe whenever possible.