zip files could be anything from a custom kernel, boot, recovery, MODs or full custom ROMs.
Xiaomi as promised started rolling MIUI 8 Global Stable build for various supportive devices. The flashing procedure can also be carried out directly through the Fastboot binary in such cases, the Fastboot ROM is compatible with Windows, Linux, and macOS. tgz file extension and require a Windows computer for installation with the MiFlash tool. Fastboot ROMs can manually install MIUI software updates and unbrick devices by restoring the stock MIUI software.
Head to Xiaomi’s official product authentication page.