In early 3D hardware, the Z buffer was a bit more special cased than it is now, where you quite literally allocate a texture. In either case, the interesting (a

In early 3D hardware, the Z buffer was a bit more special cased than it is now, where you quite literally allocate a texture. In either case, the interesting (and expensive to emulate in software) part is of course using the depth buffer to perform depth testing, that is, rejecting pixels that would be hidden.