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Bugs:Game Boy Bootstrap ROM
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This page details bugs of Game Boy Bootstrap ROM.
Nintendo Logo Integrity Exploits
Due to a bug, some bootleg games running on an official Game Boy with an official boot ROM can still get through to the game with an invalid logo.
The Game Boy reads the Game Pak's logo twice: once when displaying it, and again to compare it with the copy in the boot ROM. If the logo on the cart changes in between the two reads, the game can still boot with a bad logo.
The Game Boy Color Bootstrap ROMs only read the logo from the Game Pak once, but only the top half of the logo is checked. Hence, bootleggers could have games boot with custom logos consisting of a combination of the bottom half of the Nintendo logo and their own logo.
(Source: taizou, Ura Yukimitsu)
