Can anyone explain how storage is organized on devices with a dedicated microSD slot? When you insert a card, do all files automatically go there? Or does the system decide what goes where? Are there any performance or access quirks with this kind of memory?
Where is the data stored on a smartphone with a flash drive?
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Just like in laptops with an additional hard drive, where system files stay on the SSD while movies or games are stored on the HDD, smartphones with microSD cards follow a similar logic. Android OS doesn’t "decide on its own"—it gives you the choice: use the main storage for apps and system data, while offloading media files, documents, or even moving individual apps to the microSD (older Android versions supported this via an adapter, but Google has since restricted this feature).
For example, take the Samsung Galaxy A52s with Android 13—when installing a new game, the system will ask where to place the app: internal storage or the SD card. But if the card doesn’t support exFAT (as in newer models), you might run into issues with large file writes or crashes during copying. Some Chinese models (like Xiaomi with MIUI) force part of the data onto the microSD, but that’s more of an exception.
I had a similar experience when I was experimenting with memory partitioning on my old Sony Xperia Z with a SanDisk Ultra 128GB card. It turns out Android (or rather, its implementation on a specific device) isn't that simple. When you insert an SD card, it's used by default as an extension of internal storage unless apps support moving data to the card. For example, cameras usually ask where to save photos—internal storage or the card—but messengers like Telegram or WhatsApp still pull data to the main storage, no matter where the SIM or SD card is installed.
Performance is a sore spot for me personally. When I tried moving Asphalt 9 to the microSD, I realized the card's read/write speeds were an order of magnitude slower than the internal eMMC. The on-screen gamepad never appeared, and menu lag became constant. After moving it back to internal storage, everything ran smoothly—4K playback without stuttering. So my advice: if an app is demanding, it's better to keep it in the main storage.