Originally Posted by FreePlay

The downgrader uses a method similar to that of the 2.50/2.60 downgrader. At first it was considered impossible, as there was no IPL writing code for 1.00 (since it comes in the update EBOOT file). However, they discovered they could out patch the file so that it would write the 1.00 IPL instead of the 1.50 IPL, thus making it possible to load 1.00!