PS2:FMCB

Free Memory Card Boot, also known as FreeMCBoot or FMCB, is a method of softmodding the PlayStation 2's memory card to load and install homebrew software on boot. This method, in comparison to modchipping, is not permenant, and easy to install and use. It is incompatible with models SCPH-9xxx, also known as the "Super Slim" models. Every other model of PS2 is compatible with the exploit.

Installing FreeMCBoot
While installing FMCB does not require you to fiddle with internals, it does require the user to find a way to access the PS2's memory card, which has a proprietary connection. There are many methods to install FMCB to a stock card.

Pre-Configured Card
This is, without a doubt, the easiest way to get FMCB- a memory card with the software already installed. You can either buy one from a reputable ebay seller, or ask a friend with a modded PS2 to do it for you. There is no futher setup past this point- just plug in the memory card, turn the PS2 on, and FMCB will boot as normal.

Memory Card Adapter + Windows/Linux PC
This method uses the PS3MCA, an official adapter for PS1/PS2 memory cards that plugs into a standard USB port. It was originally designed for use on the Playstation 3, but can easily be used on any Windows or Linux PC to install FMCB.

https://www.ps2-home.com/forum/viewtopic.php?f=11&t=297

FreeDVDBoot (Disc Exploit)
This is the newest method of installing FMCB to a memory card, and utilises a backdoor in the PS2's disc authentication chip (also known as the MECHACON) to load a third-party program from a burned DVD-R. This method is proven to work on many models of the 'slim' PS2, but support for 'fat' PS2s is spotty. This requires a blank DVD-R, a memory card, and a working disc drive on your PS2.