All our images are digitally signed and therefore it's possible to check theirs authentication. You need to unzip the download package and issue those commands (Linux):
**Important note:** Make sure you use a **good & reliable** SD card. If you encounter boot or stability troubles in over 95 percent of the time it's either insufficient power supply or related to SD card (bad card, bad card reader, something went wrong when burning the image). Armbian can simply not run on unreliable hardware so checking your SD card with either [F3](http://oss.digirati.com.br/f3/) or [H2testw](http://www.heise.de/download/h2testw.html) is mandatory if you run in problems. Since [counterfeit SD cards](http://www.happybison.com/reviews/how-to-check-and-spot-fake-micro-sd-card-8/) are still an issue checking with F3/H2testw directly after purchase is **highly recommended**.
7z and zip archives can be uncompressed with [7-Zip](http://www.7-zip.org/) on Windows, [Keka](http://www.kekaosx.com/en/) on OS X and 7z on Linux. Images shall only be written with [Etcher](https://www.etcher.io) on all platforms since unlike other tools Etcher validates burning results **saving you from corrupted SD card contents**.
Also important: SD cards are optimised for sequential reads/writes as it's common in digital cameras. This is what the *speed class* is about. And while you shouldn't buy or use any card rated less than *class 10* you should especially take care to choose one that is known to show high random I/O performance since this is way more performance relevant when used with any SBC. Even cards advertised as being 'high speed' can show horribly low random IO performance in reality.
In case you chose an SD card that was already in use before please consider resetting it back to 'factory default' performance with [SD Formatter](https://www.sdcard.org/downloads/formatter_4/) before burning Armbian to it ([explanation in the forum](https://forum.armbian.com/index.php?/topic/3776-the-partition-is-not-resized-to-full-sd-card-size/&do=findComment&comment=27413)). Detailed information regarding 'factory default' SD card performance:
Login as **root** on console (HDMI / serial) or via SSH and use password **1234**. You will be prompted to change this password at first login. You will then be asked to create a normal user account that is sudo enabled (beware of default QWERTY keyboard settings at this stage). Please use [this tool](http://angryip.org/), to find your board IP address.
On Allwinner devices after switching to boot from NAND or eMMC clearing the boot loader signature on the SD card is recommended: `dd if=/dev/zero of=/dev/mmcblkN bs=1024 seek=8 count=1` (replace `/dev/mmcblkN` with the correct device node -- in case you run this directly after `nand-sata-install` without a reboot in between then it's `/dev/mmcblk0`). When booting from eMMC to get SD cards auto-detected on Allwinner legacy images please consider changing `mmc0`'s `sdc_detmode` from 3 to 1 in the board's fex file (see [here](http://forum.armbian.com/index.php/topic/1702-orange-pi-plus-2e-where-is-16ghz-and-sd/?p=13163) for details).
