It sounds more like the I/O firmware was running on dedicated PS1 hardware: https://www.theguardian.com/technology/2013/dec/12/ps4-and-xbox-one-so-why-arent-th

It sounds more like the I/O firmware was running on dedicated PS1 hardware: https://www.theguardian.com/technology/2013/dec/12/ps4-and-xbox-one-so-why-arent-they-backwards-compatible https://www.theguardian.com/technology/2013/dec/12/ps4-and-x... > The PlayStation 2, meanwhile, had the original PlayStation chipset built in, so it ran pretty much any PSone title – and when that chip wasn't being used for backwards compatibility it doubled as an input/output processor, which was pretty canny.