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M.2 vs PCIe: Pros, Cons & Differences (Especially for SSDs)

Upgrading or building a PC and wondering how M.2 components stack up against PCI-e? We can help!

We’ve put together this quick guide to cover everything you need to determine exactly which of these two options will work best for your PC, especially when dealing with SSD’s.

How M.2 Compares to PCIe

A PCI-e slot side-by-side with an M.2 drive / Christian Wiediger / Shutterstock

Unlike PCI-e, which is solely a family of connectors, M.2 can refer to both a type of connector and a form factor. The M.2 form factor, previously known as the Next Generation Form Factor, refers to a type of expansion card designed to replace the PCI-e Mini card standard.

Components with the M.2 form factor are much smaller than PCI-e alternatives, which makes them particularly useful in small devices like laptops and tablets, but they also tend to be more expensive than their larger cousins.

The M.2 form factor can technically be used with Wi-Fi, Bluetooth, NFC, and other devices/functions, but it’s most commonly used with solid-state drives (SSDs).

Though M.2 SSDs tend to be more expensive and can’t hold as much data as 2.5-inch or mSATA models, the form factor’s tiny dimensions let it fit in space-constrained devices and motherboards too crowded for larger components. And while the form factor is impressive on its own, it’s only a part of what makes M.2 a step up from previous standards.

Samsung M.2 SSD
A Samsung M.2 SSD / Ruslan Lytvyn / Shutterstock

The real advantages that come with M.2 over PCI-e have to do with M.2 slots’ connection capabilities, not the form factor.

Most new motherboards have at least one M.2 slot, and there’s a lot going on inside those little ports. Instead of accepting one kind of connector, component, or interface, M.2 slots provide a one-stop shop for all your computer’s component connection needs.

M.2 connectors are compatible with PCI-e ports (3.0 or newer), PCI-e NVMe, SATA (3.0 or newer), and USB 3.0 ports, enabling them to support a wide range of functions and making them (theoretically) compatible with a huge variety of devices and motherboards.

Compatibility with NVMe-enabled PCI-e ports is a big advantage in itself, especially when it comes to SSDs.

M.2 SSDs are currently the most popular implementation of both the connector and the form factor. On top of their compact size and ability to plug directly into the motherboard (as opposed to the cable connectors found on HDDs and standard SSDs), M.2 SSDs can also be configured to work with SATA, PCI-e, and PCI-e NVMe.

This means they’ll fit right into most existing systems. And, generally, an M.2 component will be mostly plug-and-play, but it’s an easy fix if it doesn’t show up.

While that broad compatibility is important, however, the ability to interface with PCI-e NVMe is significantly more impactful.

A standard PCI-e port provides data transfer speeds as much as six times faster than SATA interfaces, and NVMe-enabled PCI-e ports offer even faster transfers. NVMe SSDs are faster than any other internal storage media on the market today, and most of the available models come in the M.2 form factor. You can find some 2.5-inch NVMe SSDs, but they’re uncommon enough that it wouldn’t be a stretch to call NVMe compatibility a big, semi-exclusive feather in M.2’s cap.

M.2 vs PCIe Products & Compatibility

Ekkaphan Chimpalee / Shutterstock

Many more components are compatible with/plug into PCI-e ports than M.2 ports. Check out the lists below to get a sense of what works with what.

Existing M.2 Compatible Components:

  • Solid State Drives

Theoretical M.2 Components/Uses:

  • Wi-Fi Cards
  • Bluetooth
  • Near Field Communication
  • Satellite Navigation
  • Digital Radio
  • Wireless WAN

PCI-e Compatible Components:

  • Graphics Cards
  • Hard Drives
  • Solid State Drives
  • Wi-Fi
  • Ethernet Hardware

We can’t compare theoretical products to existing ones, but we can compare the one category where PCI-e and M.2 overlap: Solid state drives.

M.2 SSDs vs PCIe SSDs

There are a lot of SSDs on the market, so instead of comparing all of them we’ll stick to the best-reviewed models available.

M.2 NVMe SSDs

Gammix S70 Blade M.2 SSD

1. ADATA XPG Gammix S70 Blade (Click to check current price on Amazon)

Rated 2021’s best PCI-e 4.0 NVMe SSD for serious gamers by PC Mag, this slim M.2 SSD works just as well in a laptop as it does as expanded storage for a PlayStation 5. It’s available in 512GB, 1TB, and 2TB capacities ($89.99, $129.99, and $249.99, respectively), and it boasts blisteringly fast read/write speeds of 7400MB/s and 6800MB/s, or upwards of 50 times faster than the best hard drive. On top of its stellar speeds, the S70 BLADE comes with a high-performance heat sink and the endurance to last for up to 1,480TBT (terabytes written).

Crucial M.2 SSD

2. Crucial P5 Plus (Click to check current price on Amazon)

PC Mag rated the P5 Plus as the best mainstream PCI-e 4.0 NVMe SSD of 2021, and it’s not hard to see why. The P5 Plus comes in 500GB, 1TB, and 2TB capacities ($89.99, $159.99, and $299.99, respectively) and sports respectable 6600MB/s and 5000MB/s read/write speeds. It’s a bit slower than the S70 BLADE and doesn’t have quite the same endurance ratings, but there’s no shame in coming in second.

PCI-e SSDs

The M.2 NVMe SSD has taken over the market in terms of price, popularity, and performance to the point that finding a non-M.2, non-SATA SSD has become a real challenge. Neither of the following models are featured in any “best of” lists or found on many shelves, but they’ll at least give you a sense of how different M.2 SSDs are from their 2.5-inch brethren.

1. Wintec 2.5-inch PCIe (Gen 3.0×4) NVMe SSD (Click to check price from Wintec)

Available in capacities from 240GB to 2TB, these SSDs offer a nice middle ground between SATA SSDs and faster, slicker M.2 SSDs. Their PCI-e 3.0 connectors limit their read/write speeds to up to 2800MB/s and 1550MB/s, respectively, but what they lack in speed they make up for in endurance. Wintec has employed a range of proprietary software and architectures to make these SSDs last as long as possible, and their hard work has given these SSDs an endurance rating of up to 2793TBW, perfect for long-term enterprise use.

2. Monarch U.2 2.5-inch PCIe Gen 3×4 NVMe SSD (Click to check price from Monarch)

These SSDs offer much the same performance as the Wintec SSD above; their read/write speeds clock in at 2800MB/s and 1550MB/s, respectively, and their mean time between failures is rated at over 2 million hours, which is roughly comparable to the Wintec’s 2793TBW. They’re available in 256GB, 512GB, 1TB, and 2TB capacities, but an error on M-Factor’s website makes it difficult to figure out how much they cost.

PCIe Strengths & Weaknesses

PCIe Slots on Motherboard
daniiD / Shutterstock

PCI-e (sometimes written as PCIe) stands for Peripheral Component Interconnect Express. A PCI-e slot is what you use to connect a high-speed component to a motherboard. There used to be a number of different expansion bus (connector/data conduit) standards on the market, but all that changed when PCI-e was introduced in 2003. Nowadays you’d be hard-pressed to find a motherboard without some version of PCI-e connectors, and the same is true for most components.

It sounds complicated—and it is—but it really boils down to that pretty simple concept.

PCI-e slots typically come in five different configurations: x1, x4, x8, x16, and x32. The numbers that come after the ‘x’s refer to the number of lanes in each slot, which helps determine how much data the slot can transfer to and from the motherboard. Each lane can transfer a certain amount of data per cycle, so more lanes equals more bandwidth and faster data transfers. Different components require larger or smaller slots—GPUs typically require an x16 slot, for example—and the number and size of a motherboard’s PCI-e slots determine the kinds of components you can install in a computer.

A motherboard can also constrain your computer if its PCI-e slots are of the wrong generation. The PCI-e standard has been improved and tweaked a number of times over its 19-year lifespan, and each successive generation has come with significant improvements. The original standard, PCI-e 1.0, boasted a maximum bandwidth of 8GB/sec. PCI-e 2.0 came out four years later with a maximum bandwidth of 16GB/sec, and was only eclipsed by the 2010 debut of PCI-e 3.0, which topped out at 32GB/sec.

The current standard, PCI-e 4.0, came out in 2017 with a massive 64GB/sec bandwidth, but it’s taken some time for manufacturers to catch up. So though many motherboards made between 2017 and now have PCI-e 4.0 ports, many components are still listed as PCI-e 3.0 compatible. That doesn’t mean it’s a bad idea to get a motherboard with PCI-e 4.0 slots, however; PCI-e generations are forward and backwards compatible, meaning a PCI-e 3.0 component will work just fine if you plug it into a PCI-e 4.0 slot, and vice versa. The only downside to doing this is that the component in question will work at PCI-e 3.0 speeds, not PCI-e 4.0, so you’ll miss out on all that added bandwidth.

Final Thoughts & Recommendations

To sum it up again, PCI-e is a class of connector used in just about every computer out there. M.2 is a type of connector, too, but it’s also a form factor characterized by small, slim components that fit in space-constrained computers, laptops, and tablets. M.2 ports are mostly used for M.2 NVMe SSDs, the fastest storage media on the market, while PCI-e ports are used for a much wider range of components.

The popularity of M.2 NVMe SSDs makes it difficult to compare them to 2.5-inch PCI-e SSDs (there really aren’t many out there anymore), but it’s safe to say that you’ll want to look in the M.2 category if you’re in the market for a blazing-fast SSD.

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