What really happens when your phone runs out of RAM?

These days, High-end smartphones And even less expensive models are sent by about as much RAM as a modern mid-tone PC. And why shouldn’t they? We use our phones for different tasks, from flicking through countless apps to playing the latest high-end games. They all need RAM, and more and more of it, especially when it comes to chatting with a large language model or using AI to spruce up our media.

Can the phone even run out of RAM these days? It sounds unlikely, but I put it to the test.

In theory, it is possible to run out of RAM; If you throw enough large applications on Os at once, it is technically possible to hit that limit. But what happens in these cases? Well, Logic says the apps will be forced to close, they can hang, or that the entire operating system can not be responding. But it is very unlikely to happen, and I tested this to prove it.

To keep Android going evenly and responsive, OS has a few tricks before it starts to kill apps you may want to get back to quickly.

The first is compressive apps already in RAM using Zram. Zram is basically a compressed block of data living inside your RAM. It grows and shrinks dynamic, compresses memorial sites to save space and decompress them when needed. The app memory that is not needed is pushed seamlessly and pulled to Zram even before the phone starts to go low in memory.

All Android devices use Zram, with OEMs, able to set how large this compressed pool can grow to balance performance and response. The catch is that Zram is still using real RAM, so compression of many things does not always frees up as much memory as you can expect.

If Zram is filled up, Android is trying a couple of things to: Kernel’s swap (KSWAPD) swap process will try to rinse the memory that can be re -loaded from storage, as this can be quickly recalled when needed. If you can’t, it can kick more pages out of Zram or, if available, pushes the memory to a switch file on your phone’s storage.

However, the use of physical exchange storage is not part of the Android stock. Custom rooms –s and some OEM “Virtual RAM” implementations have dipped in the use of file file, but this is the exception and not the rule. If everything that is exhausted is terminated idle applications to allow for active processes. However, exactly how phones handle this process varies from a unit producer.

I recently had the pleasure of using Samsung Galaxy S25 Ultra With 12 GB of RAM on board, which gave me the perfect opportunity to test how Samsung’s Ram Plus management system works in the real world. I also have Xiaomi 15 Ultra, which boasts “Memory Extension” technology to increase your phone with extra memory.

My first question was: Stoles Ram Plus at traditional zram or actual swap space? This is a central distinction, partly because Samsung published a research assignment from 2023 On an “adaptive switch” ide that utilizes both the zram room and slower switching response to try to achieve the best of both. Samsung’s Ram Plus setting menu also says it “uses the phone’s storage space to give virtual memory,” which absolutely suggests switching switches, even though it is not explicitly mentioned.

However, adjusting the RAM Plus settings on the Galaxy S25 Ultra shows no changes to Flash storage partitions or mention of exchange spaces via ADB shell commands that /Proc/partitions or df -h. This strongly indicates RAM Plus only affects the Zram target size, not on storage change. This does not mean that no Samsung phones use switching, but the Galaxy S25 Ultra does not.

However, adjustment Xiaomi 15 Ultra’s “Memory Extension” option sees a reduction of free space in /data and /storage/emulated Catalogs (which are the same thing, only referred to differently). Although I cannot track exactly where this extra storage is used without rat access, the changes to the restart match the exact amount demanded by the memory extension. At the same time, the total Zram pool remains to 16 GB regardless of the setting.

Why does an exchange have at all?

Back to the Samsung, the RAM Plus setting only changes the amount of compressed barter memory (ie how much data the system is trying to keep compressed in Zram) instead of the raw size of the Zram blocker unit. As more data is compressed, Zram uses more real RAM, which depends on the compression ratio, which varies with what is compressed and the algorithm used.

A higher RAM plus setting (eg 8 GB) means that more apps stay alive in the background, but with potential decline due to extra compression. A lower setting (eg 3 GB) prioritizes speed at the expense of app storage.

On the S25 Ultra, Samsung does not let you go under a 3 GB Zram target, even if you disable Ram Plus, which makes sense with 12 GB of physical RAM since Zram probably won’t use more than 1 GB anyway. However, this may not be the case for all Samsung’s phones, especially budget models that have less RAM.

But if Ram Plus is just a variant of RAM use, why even bother to give the user control over it in the first place? Well, it’s a small but sometimes tangible difference. In short, the option exists, so you can choose whether your device will favor the Retention Background app (Bigger Zram) or Just -in -Time Responsivity (Less Zram) -all with a simple slider instead of digging into core parameters.

Xiaomi 15 ultra has very different behavior; The hand set always fixes up to 16 GB of memory to compress, but the amount stored in Zram is supported by extra swap space to avoid killing apps in extreme use cases. Unfortunately, I am unable to track exactly when compressed memory is kicked over to Flash storage, but I imagine that there will only be once a fixed amount of RAM is recorded. With 16 GB of RAM on board, it will probably be quite challenging to kick the phone to use the swap. The disadvantage is that compression and decompression from storage are slower than RAM, even with today’s fast UFS storage.

To see how all this works under pressure, I stressed both phones by gradually uploading them with apps and looking at what happened to RAM and Zram use. Finally, I overloaded the browser to consume 8 GB of RAM. It is worth noting that Flash SWAP and Zram are considered “Swaptotal” for Android’s RAM lead, which means it is impossible to see exactly when or how much change room phones such as Xiaomi use (at least not without messing the phone).

The results are pretty much in line with what you expect. Running a few small applications comes nowhere near emphasizing the Galaxy S25 Ultra’s Hefty 12 GB RAM, and Xiaomis 16 GB does not break sweat. Zram use is light and tiles in and out of real-time compacting some background tasks, but we talk dozens of MBs. There is certainly no need for exchange space here. While in this condition, it is seamless to switch to and from apps, without delay and no data loss.

It is only when we have multiple games and apps that run at once that free RAM is sinking below 4 GB and RAM control begins to ramp up. It varies depending on the workload, but Zram use can hit high MB and even a GB or more. Still, games do not need to load again, but I was kicked out of one or two active sessions, and web pages had to be updated. Still, I experienced nothing approaching a larger system slap, even with several games uploaded. As we have said before, 12 GB is absolutely plenty of RAM. Outside innovative, niche ai workloads, I guess.

Android’s standard RAM leadership is very robust, then. I had to artificially bring things to end with a 4 GB website to force everything approaching a mass emission of applications. Even then, A user interface Remained snapped, and so did Xiaomi’s Hyperos. However, most major applications had closed at this time, forcing me to load them from scratch to start them again.

When you hit the RAM wall, Android simply begins to close free apps. And thanks to Zram (and prey, if used), that wall is far away in most real cases. But most importantly, it is almost impossible to approach this point in regular use, thanks to Zram compression. Phones that use extra space price even better when it comes to keeping apps open, but not feeling as responsive as just implementations of Zram. Not that I could notice on Xiaomi 15 ultra, but it is probably an indication that 16 GB is simply overkill for even a large number of mobile applications.

One last note: SWAP does not replace Zram – it complements it. You will not tear down your flash memory to write for physical storage by activating it; It only gives less wear over time. What may be a little more noticeable is that it is a little slower to get back removing background apps from storage than decompressing from RAM, but at least you do not need to upload them.

When RAM capacities continue to rise and Android’s memory sting is getting smarter, it can never be important to change space. Still, it can be a useful tool for budget or ai-heavy devices.