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M.2 vs SATA: Storage Showdown

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SATA is a well-known technology in data storage circles, but what about M.2?

It's common to encounter M.2 solid-state drives (SSDs) while browsing a vendor's website or the virtual shelves of an online store. They typically lack enclosures — although many accessory makers offer cases for external use — and look like a cross between a memory stick and a small expansion card, complete with exposed chips some of which may be covered by a big sticker from the manufacturer.

What's the difference between these two storage technologies? 

The short answer: M.2 supports multiple storage and non-storage use cases and is therefore more of a form factor and connector specification for computers. SATA, meanwhile, is a bus interface strictly for data storage devices.

But there's more to the story. Here's what IT professionals should know about M.2 and its connection to SATA.

What is M.2?

The M.2 specification allows device makers to fit flash storage modules into thin and light devices, like today's razor-slim notebook PCs, that may struggle to accommodate a typical 2.5-inch SSD. But M.2 isn't exclusive to portable PCs.

M.2 sockets can also be found on many server and desktop PC motherboards. Formerly called Next Generation Form Factor (NGFF), the M.2 specification is considered a successor to the mSATA standard, although SSDs of the latter type are still being sold.

In terms of both storage space and physical dimensions, M.2 SSDs come in a variety of sizes. As usual, data capacities are denoted by a number of gigabytes (GB) or terabytes (TB), while the physical space taken up by the part is represented by a four or five-digit number.

In April 2018, South Korean electronics giant Samsung launched its 970 EVO M.2 SSDs with storage capacities of up to 2TB. This M2 SSD happens to be a 2280 part, meaning it measures 22mm by 80mm. Although 22mm-wide M.2 modules are the norm, the M.2 standard supports various widths (12, 16 22 and 30 mm) and lengths (16, 26, 30, 38, 42, 60, 80 and 110 mm).

Spotting an M.2 slot on a motherboard can be a new experience for users who are accustomed to fitting SSDs into a system's drive bays or expanding their PCs with PCIe cards and RAM modules.

Typically, M.2 slots are arranged so that the SSD lies flat or parallel to the motherboard, with nearby mounting posts used to secure the part with a screw. Some motherboards support a perpendicular orientation, enabling the use of an M.2 SSD with an adapter. Once snapped into place, the system will consider it yet another drive, which can be formatted, assigned a drive letter and other common storage setup tasks.

Apart from its compactness, M.2 is also a flexible connector.

M.2 not only supports SATA, but also PCIe (Peripheral Component Interconnect Express), although not at the same time in a given M.2 SSD. It even supports USB 3.0, Bluetooth, Wi-Fi and Near-Field Communication (NFC) in certain configurations.

Upon closer examination of an M.2 module, users may notice that there are notches, or keys, where the connector pins are located, yielding asymmetrical pin configurations. These determine which interface the M.2 module uses and the bus (PCIe, USB 3.0, etc.) that it can connect to. It's also a design that prevents slotting an M.2 card into an incompatible interface or placing it in a reverse configuration.

M.2 SSDs are capable of attaining high data transfer speeds, but it all hinges on the type of storage interface used.

A SATA-based M.2 SSD is limited by SATA's maximum limit of 600 MB/s (megabytes per second). An M.2 SSD that supports PCIe enables it to use NVMe (Non-Volatile Memory Express), a low-latency host controller interface specification that reach speeds of up to 4 GB/s (megabytes per second), delivering comparatively blistering performance on compatible motherboards.

What is SATA?

SATA, the acronym used to describe the common Serial Advanced Technology Attachment bus interface, is used to connect SSDs, hard disk drives (HDDs) and optical drives and is a storage industry staple.

It has largely dethroned PATA, or Parallel ATA, storage technology partly due to its thinner, more user-friendly cabling and sprightlier performance characteristics. As mentioned earlier, SATA can reach speeds of up to 600 MB/s whereas PATA tops out at 133 MB/s.

SATA wasn't always capable of reaching those speeds, although it handily beat PATA out of the gate. When it was introduced in 2000, SATA I or 1.0, was able to transfer data at a rate of up to 150 MB/s. Since then, there have been a number of performance-enhancing revisions. Today, SATA 3 SSDs are inching closer to that aforementioned top speed of 600 MB/s.

There's also revision 3.2 from 2013. Supporting both SATA and PCIe in the SATA Express specification, it was created with speeds of up to 1,969 MB/s in mind. Not to be confused with eSATA or External Serial Advanced Technology Attachment, SATA Express has not caught on with SSD makers.

Other highlights include hot plug support, allowing users to attach or remove a SATA storage device from a system while it is still running with no ill effects, and the Advanced Host Controller Interface (AHCI) interface compatibility. AHCI allows for hot plug support and a drive optimization technology that improves performance called native command queuing (NCQ).

The SATA standard is maintained by the Serial ATA International Organization (SATA-IO, or), a nonprofit supported by many IT heavyweights. Backers include AMD, Dell, HPE, Intel, Micron, Seagate and many other IT vendors.

Key differences between the M.2 and SATA

While there appears to be some overlap between M.2 and SATA, crucial differences separate them.

As noted above, M.2 supports multiple storage and non-storage use cases and is therefore more of a form factor and connector specification for computers. SATA, meanwhile, is a bus interface strictly for data storage devices.

Both terms should not be used interchangeably. Although the term "M.2 SSD" may imply a SATA-based version of a module, it's not a given. Remember, M.2 can support both the SATA and PCIe storage interfaces, but again, not both in the same module.

Another crucial difference between the two is important to keep in mind while performing system maintenance and upgrades. Although SATA devices are hot pluggable, attempting to attach or remove an M.2 SSD of any type while a system is still running is ill-advised.

M.2 and SATA Storage Performance

For speed comparisons, looking at the latest offerings from top-tier flash storage provider Samsung offers a good snapshot of the current state of the market. For the sake of simplicity and since the M.2 specification wasn't designed with spinning disks in mind, SATA hard drives will be ignored.

Revisiting Samsung's recently-released 970 PRO NVMe SSD, it sports an M.2 2280 (22mm by 80mm) form factor and uses four PCIe 3.0 channels (x4). It is capable of reaching read speeds of up to 3,500 MB/s and write speeds of up to 2,700 MB/s, give or take some MB in real-world use and under varying configurations and operating conditions.

By comparison, the 860 EVO, also sporting a 2280 form factor but with a SATA interface, can hit read and write speeds of up to 550 MB/s and 520 MB/s, respectively, on par with the 2.5-inch SATA 3.0 version of the SSD that can slip into a system's drive bay.

In short, M.2 NVMe SSDs blow their SATA counterparts out of the way when it comes transferring data. Of course, this comes at a cost.

As of this writing, an M.2 970 PRO NVMe SSD with 1TB of storage space retails for $500 while the M.2 and 2.5 versions of the 860 EVO SATA SSD, also with 1TB of storage, sell for $270.

When to use M.2 SSDs

  • When performance is a priority. Have a high-end processor and demanding applications that don't like to be kept waiting for data? An NVMe-based M.2 SSD is the answer.

  • Packing a lot of flash storage into a server chassis. PCIe adapters for M.2 SSDs open up new possibilities in the data center.

  • When physical space is at a premium. There's a reason OEMs like M.2. They can add storage using a tiny card that barely takes up any room.

  • Cut down on cabling. Although SATA cables are much slimmer than their PATA predecessors, SATA-based M.2 SSDs can be used to cut the cord entirely.

When to use SATA

  • Good-enough performance. For non-critical, run-of-the-mill workloads that could benefit from a little speed boost, SATA SSDs are a good solution.

  • Widespread support. SATA has a long history with no shortage of vendors making wares for the tried-and-true storage technology.

  • It's economical. If capacity, not performance, is a priority, SATA's value proposition can't be beat.

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