No matter what type of computer you have, if you keep it long enough, you’re likely to run out of storage. There’s never been a better time to upgrade from a hard disk drive (HDD) to an SSD or from SATA to NVMe. Both internal and external SSDs have become larger, faster, and more affordable in recent years. But which is best for you: an internal or external SSD? And which is faster?

If you haven’t already done so, there are ways to increase computer storage space. It often can help the speed of your drive and we are, after all, here to talk about speed. Consider these Crucial SSDs when comparing speeds and performance:

SSD form factors

There are three primary form factors for internal SSDs: 2.5-inch, M.2, and mSATA. External SSDs are compatible with a wide range of devices through a USB cable.

Internal SSDs form factors

2.5-Inch SSDs

For more than two decades, the 2.5-inch SSD form factor has been the standard. The award-winning Crucial MX500 is a perfect example, fitting inside the drive bay of both laptop and desktop computers. Why is this standard? Because when users first began replacing their hard drives with solid state drives, SSDS like the MX500 were designed to fit the same 2.5-inch slot that housed HDDs. This design minimized the need to replace the connecting interface cables, making the transition to a higher performance drive as easy as possible.

M.2 SSDs

The smallest form factor for SSDs is M.2. It’s about the size of a stick of gum and typically supports the highest read and write speeds due to the interface. While the M.2 socket on your motherboard may interface with either PCIe or SATA (some motherboards have slots for one or both), PCIe NVMe SSDs such as the Crucial T500 are the most popular choice because of their speed advantages over SATA. 


The mSATA form factor SSD is one-eighth the size of a 2.5-inch drive and are designed to plug into an mSATA socket on a system’s motherboard. mSATA drives are used in ultra-thin and mini devices, or as a secondary drive in desktops.

External SSD form factors

Portable SSDs

Portable SSDs such as the Crucial X10 Pro are external drives that are designed for use between various devices like desktops, laptops, tablets, phones and gaming consoles. The technology inside a portable drive is not that different from internal drives — it’s the durable enclosure and USB cable interface that qualifies these drives as external. Portable drives like those in the Crucial external SSD portfolio are fast, durable, compatible and spacious.

External SSDs

Most of the time, people use the words “external” and “portable” interchangeably when describing a storage drive that isn’t installed inside a system, but rather connects through a cable (typically USB). But they are not always the same. A small number of external SSDs are not designed for portability. Instead, they are engineered to sit on a desk while attached to your computer. Sometimes these drives are called desktop SSDs, or enterprise-class external SSDs. Crucial does not currently include any desktop SSDs in our portfolio since most users prefer the flexibility of portable drives.

SSD Interfaces

We hinted that there is more to SSD speed than just form factors. SSDs also have interfaces, which means the way they connect to a system. Although there are a fair number of different interfaces, we're going to look at SATA and PCIe for internal SSDs and USB and Thunderbolt for portable SSDs.

Serial ATA (SATA)

SATA is the most common SSD interface, commonly used with 2.5-inch form factors. In fact, you’ll often hear 2.5-inch and SATA used interchangeably to describe these drives. SATA drives have been around for more than two decades and conveniently fit in the same 2.5-inch SATA system enclosures that were originally designed for hard drives. SATA uses Advanced Host Controller Interface (AHCI) command protocols that were designed for mechanical HDDs. Though the SATA interface is older than PCIe, it brought important advances to computing when it was developed, such as hot swapping abilities or the ability for users to change out drives quickly. The latest generation provides transfer rates of up to 6GB/s. 

PCI Express ® (PCIe)

Peripheral Component Interconnect Express (PCI Express) — most often known as PCIe — is a newer high-speed serial bus interface that features a smaller physical footprint. PCIe is a physical connection that transmits information and data from one device to another within the computer or between the computer and a peripheral piece of equipment. The implementation of multiple lanes for the PCIe connection is one of the most important features of the standard. A lane is a single serial data connection, similar to a SATA connection. PCIe uses four lanes for storage devices, resulting in data exchange that’s four times faster than a SATA connection. PCIe is used with M.2 SSDs.


What us NVMe and hwy is it important to PCIe? Non-Volatile Memory Express (NVM Express) — most often known as NVMe — is a communication protocol designed specifically to work with flash memory using the PCIe bus. NVMe was created to take advantage of the parallel nature of SSDs. Combined with the PCIe bus and the increased read and write speeds of NAND technology, the NVMe protocol creates faster non-volatile storage. The combination of the NVMe protocol and the PCIe connection in an SSD results in read and write speeds that are 4x faster than a SATA SSD with a SCSI protocol.



Almost every computer today has a USB connection, making it the ideal interface for portable storage drives that you’ll use on multiple computers or devices. USB connections have many different generations, such as USB-A or USB-C. Your data transfer speed will be directly affected by the USB generation and the transfer rates of the cable. USB-A interfaces are slower than USB-C connections. Adding adapters (USB-A to a USB-C drive, for example) can also slow down transfer speeds. For the fastest transfer speeds with Crucial portable SSDs such as the Crucial X9, always use the cable included in the package.


Host compatibility


Thunderbolt 3 - 40 Gb/s

USB 3.1 Gen 2- 10 Gb/s

USB 3.1 Gen 1 - 5 Gb/s


USB 3.1 Gen 1 - 5 Gb/s

USB 3.0 - 5 Gb/s

USB 2.0 - 480 Mb/s That can support 5V


Thunderbolt is an interface connection designed between Intel® and Apple® designed to connect peripherals to computers. The latest generation Thunderbolt 3 is unique due to sharing the same reversable port as a USB-C and having backwards compatibility. USB-C accessories and cables will work with a Thunderbolt 3 port, but not all Thunderbolt 3 devices will work in a USB-C port.

SSD generations

Like many other types of technologies, SSDs also improve generationally. Today, you have the option of buying Gen3, Gen4 or Gen5 SSDs for your computer. And, unlike generations of DRAM, for example, SSDs are backward compatible, meaning they’ll work in systems built for the previous generation. Just keep in mind that you will not get top advertised speeds when running a newer generation in an older computer.

So how much faster is a new generation of SSD? Gen3 SSDs top off at around 3,500MB/s. Gen4 SSDs are 2x faster, at around 7,000MB/s. The Crucial T500 Gen4 SSD is faster still, with read speeds of 7,400MB/s. Gen5 drives, the newest available, are blazing fast. The Crucial T700, which launched as the fastest SSD on the planet, advertises read speeds of 12,400MB/s. That’s more than 3.5x faster than the Gen3 drives!

As expected, newer technology is more expensive, so it’s always important to consider what the right price/performance ratio is for your particular needs.

How to speed up your existing SSDs

Several other factors can contribute to the speed of your SSD. Always make sure your storage, firmware, TRIM, and drive health are all up to date to help keep your SSD running fast.

For most drives, we recommend keeping 10-15 percent of your drive free to balance performance and storage. Writing speeds can slow down if your drive is near or at full capacity. Some newer drives, such as the Crucial X9 Pro and X10 Pro, have improved performance, allowing for fuller speed transfer throughout the drive’s capacity.

Keeping your firmware updated helps your SSD run at peak performance and ensures technical issues are corrected.

All Crucial SSDs are designed and tested with the assumption that TRIM will be used on the computer’s operating systems, however not all operating systems support it. If your system doesn’t support TRIM, think about upgrading to one that does.

Use a self-monitoring, analysis, and reporting technology (SMART) system such as Storage Executive to track the health of your Crucial portable SSD.


So, which is faster? It really depends on what you’re comparing — your system, your SSD’s generation, form factor and interface. While the latest external SSDs have incredible write speeds, they cannot reach those speeds using older connections such as USB-A. Likewise, drive speeds are directly affected by the interface. The speed will also differ if you pair an M.2 with PCIe or SATA. And, obviously, comparing the performance of a PCIe Gen5 NVMe M.2 drive to a 2.5-inch mSATA or older external drive, you will see a wide difference in speed.

The most important aspect to consider is which form factor and interface is installed on your computer. It’s not easy to spot the differences between a PCIe and a SATA connection by looking at the slot on your motherboard. Check your computer specifications to see which interface and form factor it supports, or make it easy on yourself by using the Crucial System Selector or System Scanner to find an SSD that’s guaranteed* to be compatible with your computer.

In the end, there are many factors that determine whether an external or internal SSD is faster. But why choose? For the best of both worlds, upgrade your PC with a fast internal SSD and pair it with a fast portable SSD for fast transfer and data backups.


*If you use the Crucial System Selector or Crucial System Scanner to choose a product and then purchase it from, we guarantee it will be compatible with your system your you’ll get your money back with our 45-day no-hassle guarantee.


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