Enabling XMP or EXPO in the motherboard's BIOS is one of the first things all enthusiasts do after building a new PC. It's an easy way to ensure that you're getting the RAM speed you paid for, and often times doesn't compromise stability. They stand for eXtreme Memory Profile and Extended Profiles for Overclocking, and are different flavors of RAM overclocking validation for Intel and AMD, respectively.
When turning on XMP, you might notice that there are multiple different profiles that one can choose between, often at least 2, but sometimes even more than that. There isn't a lot of difference between them, and while most users will be totally fine choosing the first profile, there are some scenarios where you may want to try the others.
What do these profiles do?
XMP and EXPO are simple ways to overclock memory
Fundamentally, XMP and EXPO are nothing more than a simple, one toggle overclock for your memory. When you buy RAM, whether its DDR4 or 5, it will often have advertised speeds that are well above the minimum spec for that specific type of memory. For DDR5, this is 4800 MHz, but some sticks have rates on the box that can balloon to numbers well above 7000 MHz. Instead of needing to do so manually, XMP and EXPO allow your RAM to reach these speeds with pre-loaded profiles.
What's the difference between XMP/EXPO profiles?
Speed is the main difference
XMP and EXPO profiles come preloaded onto your memory and can be enabled in your BIOS. These profiles can differ primarily in speed and timings, and that's where all the performance differences will be felt. Another difference you might find between profiles is in voltage, which will have a modest impact for most users on desktop systems, but it can be the reason for a particular profile not playing nice.
Which XMP/EXPO profile does what will not only vary between RAM kits significantly, but also varies depending on motherboard vendor. Some vendors, like ASUS, will load "profiles" that are optimized for their boards that aren't the same as those burned into the DIMMs themselves, so it's difficult to say exactly which profile does what, but in general, the first profile will be the fastest speed your kit supports, and the second will be at a slightly slower speed.
When should you use the other profiles?
The first profile is what most people should use
Typically, most RAM vendors will put the spec you see on the box in the first profile. For instance, if you purchased RAM that says it's rated for 6000 MHz, the first XMP/EXPO profile will have that speed loaded. This is what most users load when they enable XMP using the simple "Enable/Disable" toggle in their motherboard's BIOS, and it's the one that the vast majority of users will be just fine with.
The other, often slower profile, should be used if you're experiencing any kind of instability with your system. Random crashing of applications, blue screens, or any similar symptoms can be a sign that your RAM is tuned too high. At the end of the day, XMP and EXPO are overclocking, and they do have the capacity to cause system instability.
There is a particular sweet spot for RAM speed with certain CPU architectures. For example, AMD Zen 4 plays really nicely with RAM at 6000 MHz, and anything above that sees not only diminishing returns, but can also cause system instability on certain CPUs. This is where that 2nd profile can come in. Just as a hypothetical, if my memory was causing issues at 6000 MHz at 1.35v, setting it to the slower, 5600 MHz 1.25v profile could allow my RAM to still run at well above the default spec, but not to a level where it causes instability. These "slower" profiles might also have tighter timings, which could actually have a greater performance impact than a bump in frequency would, all depending on your workload.
Test each profile and see which is best for you
The good news about XMP/EXPO is that you don't really need to overcomplicate it. The first profile will usually run just fine, especially if the memory you bought is within spec for your CPU and motherboard. If it doesn't, and you're running into stability issues, trying the other profiles can be a great way to mitigate them. If you're still having trouble, tuning your RAM manually as a last resort can help, but it's possible your issues could be caused by another component entirely.