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.
Osteocyte s have the function of supporting the tissue. osteocyte A bone cell that is character istic of adult bone, has developed from an osteoblast, and is isolated in a lacuna of the bone substance. osteon Unit of bone structure; Haversian system.