PS3 Homebrew Wiki
Master (v21.1b5)

Preparing for CFW

Due to the nature of how custom firmware works on a PlayStation 3, it's not as easy as just installing a firmware update file. Before you can do that, you have to modify certain files in your flash memory to be able to downgrade your console (that is, install CFW.)
There are many ways of doing this, and each way has its own strengths and its own weaknesses. Each option that you can choose still carries around the risk of a possible brick, so make sure to follow each tutorial down to the letter and keep backups of your NAND/NOR flash.
If you've got a console only capable of HEN, you can't use these options (because you can't downgrade to a firmware less than 3.60). If you want to read, go ahead, but DO NOT, I repeat, DO NOT ATTEMPT any of the methods described in this section if you have a non-CFW console, you will brick your console. (Unless you're using a firmware flasher to repair, that's fine.)