What type of brake system does 1990 Chevy has?

1990 Chevy vehicles used a variety of brake systems depending on the specific model (e.g., Silverado, Cavalier, Suburban, etc.). There wasn't a single system across the entire 1990 Chevy lineup. Most likely they would have had hydraulic disc brakes at the front and hydraulic drum brakes at the rear, but some models might have had disc brakes all around. To know for sure, you'd need to specify the *exact* model of the 1990 Chevy.