I believe officially, the biosensor is stated to allow the pilot to control his/her mobile suit with their mind:
Gundam Official wrote:Its full capabilities are unknown, but the bio-sensor does allow a Newtype pilot to control a mobile suit via mental commands.
Come to think of it, this does explain a few things, such as a particular scene where Kamille stands up and screams while the Zeta shoots madly into space. Don't even get me started on the random stuff Judau did in ZZ. All the fancy god-mode hacks and increased power output of weapons and thrust seem to be just a byproduct, though as Mashymre showed us, the biosensor isn't as necessary as having actual Newtype powers.
The explaination for the psycommu system is also pretty similar:
The Flanagan Institute goes on to develop a mind-machine interface called the psycommu (psycho-communicator) system, which receives these thoughtwaves and translates them into computer commands. Using this interface a Newtype pilot can direct remote weapons, and operate huge mobile armors, by thought alone.
The psycommu seems more prominant for use with remote weapons, though I do believe a few mobile suits utilize the system directly as well.
And finally, the psycoframe:
A design approach in which microscopic psycommu receiver circuits are installed throughout a mobile suit's internal frame and cockpit walls. These tiny circuits amplify and transmit a Newtype pilot's thoughtwaves, enabling the mobile suit to respond instantaneously to mental commands.
Again, it seems to work by allowing a pilot to control the mobile suit with their mind, but the description makes it seem a lot more efficient.
While this is just speculation on my part, I think that the fundamental difference between the psycoframe of Nu Gundam and that of Unicorn lies in
what they allow the pilot to mentally control. Because the psycoframe in Nu Gundam (and Sazabi) lines the cockpit, it allows Newtype pilots like Amuro to control all cockpit functions with their mind; essentially pulling levers and hitting switches through thought alone. Unicorn, on the other hand, has its entire frame composed of psycommu receptors which would allow the pilot to literally control the machine as if it were their own body (which matches its official description, I believe).