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Types of SSDs: 2.5” vs. M.2 SATA vs. M.2 NVMe vs. U.2

The primary types of SSDs are the 2.5”, M.2 (SATA & NVMe), NVMe PCIe SSD, and the U.2 (formerly SFF-8639), each offering distinct advantages and disadvantages.

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Solid-state drives (SSDs) have become the norm over bulky spinning disk hard drives (HDDs) because of their increased read/write speeds and lack of moving parts. You may have noticed that there are many types and form factors of SSDs available, so many so that it’s gotten a little confusing to suss out the differences between them. SSDs come with a variety of connectors, connection protocols, underlying technologies and form factors. The primary types of SSDs are the 2.5”, M.2 (SATA & NVMe), NVMe PCIe and the U.2 (formerly SFF-8639) SSD, each offering distinct advantages and disadvantages. This may be confusing now but this guide should clear things up!  Learn more about the types of SSDs to make an informed SSD buying decision.

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Quick Tech Specs
  • Connector: SATA
  • Connection Protocol: SATA
  • Technology: SATA
  • Form Factor: 2.5”

Description: The 2.5” SSD is the traditional form factor most of us are familiar with if you have built a computer in the past. It is typically mounted to the SSD tray within a PC tower. The 2.5” SSDs connect to the motherboard via SATA and transfer speeds max out around 500-600 MB/s. For comparison’s sake, SSDs using NVMe technology have much higher bandwidth and max out around 7000-7500 MB/s transfer speed at the time this article was written, almost 12x as fast!

Note that 3.5” form factor SSDs also exist but are prohibitively expensive for the average consumer.

Advantages: Less costly and easy to find, the 2.5” SATA SSD will work with just about any motherboard today. While not as fast as NVMe SSDs, they still are much faster than HDDs (which top out at about 160 MB/s transfer speeds) and can handle most tasks efficiently. 2.5” SATA SSDs have the additional benefit of having no moving parts, so they break much less easily than HDDs.

2.5” SSD drives are easier to remove and replace than M.2 drives since they’re separate from the motherboard and you don’t have to work around your graphics card or other components you currently have connected if you’re upgrading your current rig.

Disadvantages: 2.5” SSDs have significantly slower transfer speeds when compared to SSDs with NVMe due to bottlenecking of the SATA connection protocol and are bulkier than M.2 form factor. 2.5” SSDs also require both a SATA data cable connection and SATA power cable, which can increase cable clutter.

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Quick Tech Specs
  • Connector: M.2
  • Connection Protocol: SATA
  • Technology: SATA
  • Form Factor: M.2

Description: The second generation of mini SATA and an increasingly common SSD form factor, M.2 SATA SSDs come in a variety of sizes expressed as code. They are either 22 or 30mm wide and vary in length from 16mm to 110mm in 2022. You’ll see them sold as 2280, 1630, 3030, and so on, with the first two digits representing width and the last two or three digits representing the length of the device.

M.2 SATA SSDs have two U-shaped cutouts, or “keys”, near the edges, also known as the “M” and “B” keys. Most M.2 NVMe SSDs, on the other hand, only has 1 “M” key. There are exceptions to this, however, so be mindful of this when purchasing either storage device.

SATA bandwidth is slower than that of NVMe, but if you have an older motherboard, it may not support NVMe or PCIe bandwidths. Other motherboards come equipped with dedicated M.2 slots so you don’t have to consume SATA slots. Oftentimes, M.2 slots will support both M.2 SATA and M.2 NVMe SSDs. Make sure to check what SSD technology your motherboard can support.

Advantages: Significantly faster data transfer speeds vs. 2.5” SSDs. Can be installed in any motherboard supporting the M.2 interface, which is quite common amongst motherboards today. M.2 SATA drives are smaller than 2.5” drives--only about as thick as a stick of gum. Since they clip in directly to the motherboard, you save case space since you don’t need SATA cables.

Disadvantages: M.2 SATA SSDs are slower than NVMe SSDs and not all motherboards support M.2 connectors, although most modern motherboards do. M.2 SATA SSDs transfer speeds are limited by their connection protocol, much like their 2.5” SATA cousins. They are also a little more expensive than 2.5” SATA SSDs today.

Additionally, it can be inconvenient to install or replace an M.2 in an existing build since you’ll need direct access to your motherboard and may need to work around or even remove other components to install it.

Quick Tech Specs
  • Connector: M.2
  • Connection Protocol: PCIe
  • Technology: NVMe
  • Form Factor: M.2

Description: NVMe stands for Non-volatile Memory Express, characterized by high bandwidth and very fast transfer speeds. “Non-volatile” memory indicates that being powered is not a requirement for this device to retain stored information.

To contrast, RAM or DRAM is “volatile” memory storage so once power is cut, the data is lost.

Read/write speeds of the top NVMe SSDs on the market can exceed 3000 MB/s (3 GB/s), with some Gen 4 NVMe PCIe SSDs capable of 7500 MB/s. The top SATA SSDs clock in around 550 MB/s, so NVMe SSDs are far and away the fastest transfer speeds for any SSDs on the consumer market.

You may see reference to “lanes” when purchasing M.2 NVMe SSDs. Basically, more lanes equals both a longer SSD and faster transfer speeds, with one lane equal to about 1 GB of transfer speed. A 4 lane NVMe SSD will have twice the bandwidth than a 2 lane NVMe SSD. Most 4 lane M.2 NVMe SSDs have one key, unlike the M.2 SATA SSDs which have two.

However (confusingly), some 2 lane M.2 NVMe SSDs have two keys, just like M.2 SATA SSDs. Be sure to carefully read the product description before purchasing either since this could impact your ability to connect the SSD to your motherboard. Also, check the transfer speeds—if speeds exceed 550MB/s, you’re looking at an M.2 NVMe SSD and not a M.2 SATA SSD.

Advantages: M.2 NVMe SSDs have the clear transfer speed advantage. They’re also smaller than 2.5” SATA SSDs due to the M.2 form factor.

Due to the PCIe connection protocol, M.2 NVMe SSDs are backward and forward compatible, so you can use PCIe 3.0 NVMe SSDs with a PCIe 2.0 system or vice-versa. However, using a PCIe 3.0 SSD with a PCIe 2.0 motherboard will reduce overall bandwidth availability. On the other hand, using a PCIe 2.0 SSD with a PCIe 3.0 motherboard will not throttle performance.

Disadvantages: The faster the drive, the more expensive. M.2 NVMe SSDs cost more than either 2.5” SSDs or M.2 SATA SSDs. Also, while motherboards may be compatible with the M.2 form factor, they may not support NVMe. Make sure to read your motherboard specs carefully before making your purchase.

Reportedly, M.2 NVMe SSDs also run hot since they’re transferring so much data so quickly. If you don’t have a solid cooling solution for your computer, you may want to install or upgrade your heat sinks before installing M.2 NVMe SSDs.

Also, not everyone needs this kind of speed! If you’re not a hardcore gamer running the latest titles with graphically rich detail and you can patiently wait for your computer to boot up, you could save a bit with a SATA SSD and have an easier time installing it if you’re upgrading your current system.

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Quick Tech Specs
  • Connector: PCIe
  • Connection Protocol: PCIe
  • Technology: NVMe
  • Form Factor: PCIe AIC (Add in Card)

Description: These SSDs are comparable in most ways to M.2 NVMe SSDs, including their lightning-fast transfer speeds. The only difference is  the way they connect to your motherboard--they utilize the PCIe slot instead of via an M.2 connector. They also are much more expensive on average than the M.2 form factor NVMe SDDs.

Advantages: If your motherboard doesn’t support M.2, just about every modern desktop PC motherboard supports PCIe. You get the rapid transfer speeds of NVMe without needing an M.2 connector, which is great for upgrading legacy systems. Due to their increased surface area, NVMe PCIe SSDs run cooler than the smaller M.2 NVMe SSDs, so overheating isn’t as much of a factor.

Disadvantages: These drives are much larger than M.2 drives and will take up one of your PCIe slots. This could be potentially problematic for installation on your existing rig if you already have a graphics card or other components connected to your motherboard. They also tend to be quite expensive due to the fact that they typically come in high capacities and are used in enterprise storage systems.

Quick Tech Specs
  • Connector: U.2 (SFF-8639)
  • Connection Protocol: PCIe/SAS/SATA
  • Technology: NVMe
  • Form Factor: 2.5”

Description: The U.2 SSD is uncommon in consumer applications and was created for rather specific use cases. With PCIe AIC SSDs, users must open a server before inserting or removing them. U.2 SSDs, on the other hand, are hot-pluggable, meaning they can be inserted with or without prior notice, like your standard SATA SSDs or HDDs.

You’ll find U.2 SSDs most commonly in enterprise servers and storage solutions since they also have a larger capacity than most M.2 SSDs and better heat dissipation due to their increased surface area. They’re compatible with 2.5” and 3.5” PCIe slots.

Advantages: These are hot-pluggable SSDs, which makes it easy for admins to upgrade their system storage. They’re also backwards compatible with HDDs and can utilize a variety of connection protocols depending on the system’s backplane. Additionally, they can operate with NVMe transfer speeds without heat being as much as a factor than with M.2 due to their increased surface area and ability to dissipate heat.

Disadvantages: U.2 SSDs tend to be quite expensive due to their special SFF-8639 connector. Some legacy enterprise storage infrastructure is unable to accommodate SFF-8639 connectors.

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We hope this assessment of the wide landscape of SSDs types and forms factors was helpful in making your buying decision. CDW offers storage solutions for small business to enterprise, as well as data backup solutions so your data center is prepared for the worst.