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.
matrix. n, pl matrices (ËmeÉªtrÉªËsiËz; Ëmae-) ËmÃ¦ or. matrixes. 1 a, substance, situation or environment in which something has its, origin takes, form or is. enclosed. (2) anatomy anatomy the thick tissue at the base of a nail from which a fingernail or toenail. developsatrix. n, pl matrices (ËmeÉªtrÉªËsiËz; Ëmae-) ËmÃ¦ or. matrixes. 1 a, substance, situation or environment in which something has its, origin takes, form or is. enclosed. (2) anatomy anatomy the thick tissue at the base of a nail from which a fingernail or toenail. develops