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.
A stellate, non-dividing osteoblast embedded in mature bony tissue. Supplement. Bone cells are found within the bone tissues, and they are responsible for the make-up of the skeleton of vertebrates. The four main types of bone cells are the (1) osteoclasts, (2) osteoblasts, (3) osteocytes, and (4) lining cells. The osteocyte is a non-dividing, stellate bone cell.