eMMC to SD Card Adapters Explained

The eMMC to SD card adapter shows up a lot in IoT devices. I have owned one for my Raspberry Pi for a while and they are fantastic.

In this article I will explain what these devices are, the main advantages of them (speed/performance) and benchmark some eMMCs to show performance differences. By the end of this article this should give you an idea if this is a type of device you’d want to work with / use.

Let’s begin!

What are they?

It’s basically a eMMC storage chip soldered onto a board that fits into a SD slot. This makes it a lot bulkier than a normal micro SD card but much less bulky than almost any other storage solution on many platforms.

Because of this I’m seeing them more and more in IoT devices. Here is one I found recently in a Helium hotspot:

Now let’s look at the back of the eMMC:

As you can see they actually had their company name / web site / everything printed onto each one of these eMMC keys essentially to use in their own products.

Connecting to PC / Device

These actually just slide right into any SD card slot. You can use them on your PC or with a SD adapter like this:

They will show up right in your PC like a regular card. Note that some SD adapters do not like these. I have a SanDisk SD to USB adapter that won’t work with the eMMC modules at all so keep in mind that some adapters might not like them. I have not found any actual SD ports though that won’t read them (it’s only a question of whether an adapter will work).

Performance Advantages

I have owned another SD to eMMC adapter for quite a while. It seems to have been removed from Amazon (some Pi resellers still have it though) and I’ll have some other recommendations later that are easier to find / obtain. It’s this one:

I benchmarked this device with two things in mind. I wanted to compare it to how fast a SD card is *and* I wanted to compare using this SD to eMMC adapter to using a built-in eMMC on the Compute Module 4.

I used my Pi Benchmarks web site for testing. The built in Compute Module 4 eMMC that is physically soldered to the board (meaning it doesn’t go through the SD card slot / port) scored 5,499 with stock clock speeds. That is extremely fast and the fastest SD cards only score about 2,000 points.

That means that a eMMC’s performance is nearly 3 times as fast as even an application class (A1) SD card. That’s very fast! Okay, so we definitely know eMMC is faster, but my next question is do you lose some of that performance by using the SD adapter instead of having it soldered directly to the Pi like the Compute Module 4?

My benchmark with the UUGear is benchmark #48189 and was 3,899 points. This means we did actually lose a little bit of speed through the SD card port and I 100% expected this. I was actually surprised though that we actually didn’t lose that much. That is still double the fastest SD cards even going through the exact same SD card slot!

Other Available eMMC to SD Adapter

Definitely check Pi resellers for the UUGear module as well!

Conclusion

It’s roughly 3 times faster than even an application class (A1) SD card. They particularly excel at random read/writes (meaning a random area of the disk is accessed rather than all in order such as when you write a large file) making them a great choice for running an operating system / applications. They’re fantastic devices.

With the attached leash they actually feel a lot like a USB flash drive people sometimes carry around with all of your utilities / files on them but it’s for a SD card slot!

As long as you can fit it into your case / project they cost about the same as a really nice SD card and perform much better. I highly recommend them!

Other Resources

If you are looking at eMMC modules for Hardkernel ODROID boards check out my ODROID eMMC guide here