First of all, an optical drive can be a CD, DVD, or BluRay drive. The button isn't invisible, it's just hidden in plain site by design. The previous pictures show its location, but here is one more. This is a picture of the top of a 660 showing 2 drives.
What is difference between an osteon and osteocyte? An osteon is the functional unit of cortical bone. Osteons contain osteocytes, which are cells that produce bone matrix.
Osteocytes are mature osteoblasts that have become trapped within the very bone matrix they produced. Osteocytes continue to form bone to some degree, which is important for maintaining the strength and health of the bone matrix.However, osteocytes perform functions that extend far beyond simple maintenance.n osteocyte is a bone-forming cell that has become entrapped within the bone matrix (the hard part of the bone). It lies within a lacuna, a small pit, and communicates with its surroundings through tiny channels called canaliculi.