It's not original dev-box BIOS
It is hacked HKT0120 dev-box BIOS v1.011.01
In fact, now it is standard BIOS, but with loading as at HKT0120.
you can find it here:
http://www.dcfan.net.ru/f<br
In fact it is an ordinary dreamcast, having on board two BIOS, original MaskRom + rewritable FlashRom,
console can work both on original and on modified BIOS, at any time, you can switch between the