A conventional, well 99% of turbo's ive ever seen regulate the boost via the wastegate. An internal wastegate is held shut by an actuator with a set pressure spring in it with a vac/boost line connected to it. The wastegate is shut completely to allow all your exhausts gasses to spool the turbo as fast as it can. If you have a 8psi actuator, The 8psi of pressure in the boostline will push the actuator spring inwards, which then pushes the actuator rod outwards and wastegate will open to a certain amount, allowing the exhaust gasses to bypass the turbine (partially) still allowing a certain amount of gasses to spool the turbo.
This is the rear of my turbo. You can see the actuator is on the left hand side. It's basically a little flap which controls the flow that bypasses the turbine.
The blow off valve on an RB motor is open under vacuum (also a spring i believe) and when boost builds, it holds it shut, so then when you back off the throttle and vac is applid then the blow off valve releases the pressure (instead of back through the turbo) back infront of the turbo and behind the AFM. This has no control over boost levels.
I hope this made any sense whatsoever.