DGStation uses several different image file-formats. These are the main ones and their consequences:

su_uboot_*.img
Bootloader (sometimes formats the HDD)

su_all.img
Complete image with bootloader

us_all_noboot*.img
Complete image without bootloader: all data will be erased(except recordings on HDD)

su_kernel_root*.img
Core image, most suitable for updates, leaves usersettings intact.

su_kernel_root_db*.img
Core image incl db.img

su_db*.img
Database update, you need to setup the STB again, so save your settings first

su_welcome.img
Replaces the usual starting picture on STB

• su states the way of transfer eg: Serial or USB. USB-files can be flashed with FTP (ftp-server or pc-editor)(only on 200s/400s).
• usb_uboot images and *_all.images must be flashed by flashtools on 400s using usb, for flashing the 200s you need a serial_uboot.img.
• If you flash a kernel_root_db, it won't change the bootloader nor the welcome.img. If you only flash the u-boot, kernel-root or welcome image, it will not affect the other parts.

More info on image difference can be found: here

Several welcome images: here