[spicyjpeg]

There are homebrew tools that can be installed on a PS1 memory card [1] and allow for executables to be loaded from a host machine into RAM through the serial port on the back of the console, in a similar way to what Sony's official Net Yaroze loader did back in the day. These tools can also use undocumented CD-ROM drive commands to disable region checks without the need for a modchip, provide semihosting (host filesystem access) and so on.

On the PS2 it's slightly more complicated, as there is no way to launch the "native" PS1 backwards compatibility mode other than to use a modchip (or firmware mod on some models) and burn the executable onto a disc; the serial port is not exposed either, making debugging much harder. It can still be done, but it's much easier to just use an actual PS1.

[1]: https://github.com/JonathanDotCel/unirom8_bootdisc_and_firmw...