While bios7.bin is a standard file required for accurate emulation, the addition of "delta" usually points to one of two things: the popular for iOS, or a Delta Patch used to modify the BIOS.
Analyzing the delta between two BIOS versions can provide insights into: bios7.bin delta
In the Nintendo DS homebrew and modding scene, bios7.bin is sometimes the subject of delta patches for two reasons: While bios7
: Launch the Delta Emulator on your iPhone or iPad and tap the Settings (gear) icon. bios7.bin delta