You might have come across the terms like old bootrom and new bootrom when checking our guides to jailbreak iPhone 3GS 4.0 (or unlock iPhone 3GS 4.0). In case you are new to all these and do not understand what they mean and wondering how to find the bootrom version, here is a simple tool for you.
iDetector is a small and simple tool developed by iH8sn0w which can tell whether your iPhone 3GS contains old bootrom or new bootrom version. Simply place your 3GS into DFU mode and click the button. iDetector only supports iPhone 3GS. iDetector comes as a boon for many since manually checking for bootrom version (iBoot) involves lot of not-so-simple steps as explained here.
Download iDetector 1.0