Every Samsung firmware has a build number — also called the PDA or AP version. It looks cryptic, but it tells you the region, whether the update is security-only, the bootloader binary, and when it was built. You can see yours in Settings › About phone › Software information › Build number.
Example: S938BXXS6CYI1
| Part | Meaning |
|---|---|
S938B | Model code without the SM- prefix (Galaxy S25 Ultra, SM-S938B). |
XX | Region group of the build (XX — Europe / global, UE, UB, ZH… — other markets). |
S | Update type: S — security patch only, U — feature update. |
6 | Bootloader binary (shown as Bit on SAMDB). After 9 come letters: A = 10, B = 11… |
C | OS revision: A for the Android version the phone launched with, B after the first major upgrade, and so on. |
Y | Year: … V = 2022, W = 2023, X = 2024, Y = 2025, Z = 2026. |
I | Month: A = January … I = September … L = December. |
1 | Build iteration within that month. |
So S938BXXS6CYI1 is a security update for the European SM-S938B on bootloader binary 6, built in September 2025.
The CSC version (e.g. S938BOXM6CYI1) follows the same pattern; OXM there is the
multi-CSC package — see CSC codes.
Why the bootloader binary matters
Samsung raises the binary when it fixes a security issue in the bootloader. The phone then refuses any firmware
with a lower binary — Odin stops with SW REV CHECK FAIL. In practice:
- Upgrading is always possible: any newer build with the same or higher binary installs.
- Downgrading works only to builds with the same binary. Once a phone has binary 7, no binary-6 firmware will flash.
- Before flashing, compare the fifth character from the end of your current build number with the Bit column of the build you want.
Older build numbers
Firmware from before about 2016 (for example I9300XXEMG4) uses a shorter format without a binary
digit, so SAMDB shows “—” in the Bit column for those builds.