Can I add internal SSD to my new MacBook Air M3 15"

There is no way to upgrade the internal SSD, or to add another. If you need more storage, look for an external USB 3.*, USB4, or Thunderbolt 3 SSD.

If you bought the MacBook Air directly from Apple, and are within the 14-day return window, you could return it, and custom-order another one with more internal storage. (Apple offers 1 TB and 2 TB storage options.)

ssm00001 wrote:

Are there any external SSDs that compare in performance with internal SSDs in terms of speed?

No. Apple silicon internal storage connections are seriously fast.

There are some I/O performance details here:

https://www.tomsguide.com/features/apple-macbook-hierarchy-m3-vs-m2-vs-m1-benchmarks

External storage connected via Thunderbolt is your fastest external alternative. Thst won’t be cheap.

Some reading:

https://www.tomshardware.com/reviews/plugable-thunderbolt-3-nvme-external-ssd/2

Depending on the details of your case, it might be cheaper to sell this apparently-under-purchased MacBook Air, and get a replacement new or used or refurb MacBook Air or MacBook Pro better configured for your current needs. Or sell this laptop and get a desktop Mac, as those usually provide more I/O connectivity than laptops if you’re not particularly using this Mac while mobile.

If you're looking for absolute speed, the closest thing to the internal SSD would be an external Thunderbolt 3 or USB4 40 Gbps SSD. Because of their speed, these SSDs may generate a relatively large amount of heat when you're using them.

So far, I've only heard about one USB4 40 Gbps SSD.

Other World Computing – OWC Express 1M2

Thunderbolt 3 has been out longer, and so there are a lot more external SSDs and "bring your own blade SSD" enclosures that use it. OWC is just one of many vendors who offer those SSDs and enclosures.

Other World Computing - External Storage

PCIe NVMe SSDs that attach via USB 3.1 Gen 2 are slower than Thunderbolt and USB4 SSDs - but can be a lot cheaper (lower-cost enclosure), and still run much faster than 2.5" SATA notebook SSDs.

Whether you'll notice a difference in speed depends on what you are doing. For some applications, even a slow mechanical hard drive is plenty fast. For others (e.g., editing high-resolution video for a Hollywood movie), you might want all the speed that you could get.

In terms of maximum available performance, there’s no difference between Thunderbolt 3 and Thunderbolt 4.

https://www.intel.com/content/www/us/en/architecture-and-technology/thunderbolt/thunderbolt-3-vs-4.html

Minimum available bandwidth is better with T4 sure, and there are some other video and numbers-of-ports advantages with T4.

And USB4 inherently includes T4.

But in terms of maximum available performance I/O performance more generally, T3 and T4 are the same.

MrHoffman wrote:

And USB4 inherently includes T4.

USB4 does not inherently include Thunderbolt 4.

The new USB4 40 Gbps transfer mode is based on technology borrowed from Thunderbolt, but there is nothing saying that a USB4 host port must support Thunderbolt 3, Thunderbolt 4, or USB4 40 Gbps. Those are optional features.

To date,

• All Apple Silicon Macs have Technical Specifications that say they support USB4.
• Only those that support attaching two USB-C or Thunderbolt displays without closing the lid have Thunderbolt 4. The others have Thunderbolt 3. My understanding is that Thunderbolt 4 certification requires the ability to drive two displays over USB-C or Thunderbolt.