Some more details (and interesting historical perspective) can be found here: https://superuser.com/questions/704920/how-to-determine-if-usb-mouse-supports-ps-2

Some more details (and interesting historical perspective) can be found here: https://superuser.com/questions/704920/how-to-determine-if-usb-mouse-supports-ps-2 https://superuser.com/questions/704920/how-to-determine-if-u... Apparently around 2014 the vast majority of mouses and keyboards were dual-protocol, but in 2019 the first reports of them being USB-only started appearing. I suspect a lot of the cheapest mouse SoCs are still dual-protocol as they worked when first designed, and they just kept producing them without any changes. Pinout and explanation of how they detect protocol here: https://retrocomputing.stackexchange.com/questions/28288/how-did-early-green-ps-2-to-usb-mouse-adapters-work https://retrocomputing.stackexchange.com/questions/28288/how...