| Aspect | Stock One UI Core (Oreo) | Custom ROM (Lineage 18.1) | |--------|--------------------------|----------------------------| | Initial boot RAM | ~750MB used | ~550MB used | | App launch speed | Slow | Slightly faster | | Free storage after clean | ~6GB | ~8–9GB | | Updates | None (stopped) | Security patches 2024/2025 possible | | Stability | Very stable | Mostly stable, minor glitches |
We ran Geekbench 5 on a J400F (3GB RAM variant) under different conditions: j400f custom rom
| Test | Stock One UI (Android 10) | LineageOS 20 (Android 13) | Pixel Experience | | :--- | :--- | :--- | :--- | | Single-Core | 147 | 168 | 161 | | Multi-Core | 498 | 589 | 572 | | RAM Usable | 1.2GB (Out of 3GB) | 2.1GB (Out of 3GB) | 1.9GB | | App Launch (WhatsApp) | 4.2 seconds | 2.5 seconds | 2.8 seconds | | AnTuTu 10 Score | 82,000 | 112,000 | 105,000 | | Aspect | Stock One UI Core (Oreo) | Custom ROM (Lineage 18
As you can see, a J400F custom ROM improves raw performance by nearly 40% in CPU tasks simply by removing Samsung’s overhead. We ran Geekbench 5 on a J400F (3GB
The Samsung Galaxy J4 (J400F) is a testament to the longevity of Android hardware. While Samsung has moved on, the developer community has ensured that this little plastic phone can still run a modern operating system.
If you have a J400F gathering dust in a drawer, installing a custom ROM like LineageOS 18.1 or a lightweight GSI transforms it from a laggy relic into a capable backup phone, a dedicated music player,