PlayStation 5 (PS5) will certainly have features that are not available in the previous generation consoles, namely backward compatibility.
As the name suggests, this feature allows users to play various games specifically designed for previous generation consoles, in this case, PS4 on PS5 consoles.
This was also briefly confirmed by Mark Cerny as the Lead System Architect for the console.
He said that the PS5 engine would have the architectural design base of the PS4 engine, but it was further developed. Thus, the PS5 can play PS4 games, because the engine architecture is indeed the same.
However, Cerny did not explain further whether PS5 will be able to play PS1 games to PS3 or not. Because Cerny only mentions PS4 only.
Previously, PS4 and even PS4 Pro did not have this backward compatibility feature.
To play PS1 to PS3 games on PS4, users can take advantage of the PlayStation Now service that allows them to play older games, through Sony’s ‘streaming’ service like watching videos.
Unfortunately, Sony has not provided more detailed information about how the backward compatibility mechanism in the PS5 will later work.