How Computers Work – Part 10 – Optical Drives [Mega Series]

You probably wouldn’t believe me, but you have a device on your computer that has has lasers and high-speed motors that use up just a couple of Watts. Such devices are better known as optical drives. Whether you have a Blu-Ray, CD, or DVD drive doesn’t matter; they all work the same, much like how all banks screw you over in the same manner with a little touch of their own personality.

From a Quarter to a Roll of Duct Tape

There’s a ton of different optical discs out there, ranging from the size of a quarter to the size of an average roll of your friendly neighborhood duct tape:

    • DataPlay Discs (500 MB Capacity – Tiny)
    • MiniCD/DVD (185 MB – 1.4 GB Capacity – Small, about 7 cm in diameter)
    • CD/DVD/Blu-Ray (700 MB – 25 GB Capacity – Large)

In this whole diverse world of optical discs, I assure you that all of the drives work in relatively the same way.

How Optical Drives Work

Each disc holds data within its plastic exterior. The shiny layer of aluminum below all the polycarbonate plastic contains fluctuations in the surface, which are then read by the drive using a laser and an optoelectronic sensor. Considering that discs spin at rates of up to 30000 RPM, the implications of this are enough to make anyone’s constipation disappear. By the way, did you notice how we are so capable of making such advances in technology and, at the same time, we can’t make a headache pill worth a damn?

Before we go further, here’s an optical drive’s guts. Enjoy:

The optoelectronic sensor is within the laser assembly, and I’m too lazy to photoshop that much. You get the point.

As mentioned earlier, a disc has fluctuations on its aluminum surface. The bumps on the surface are known as “pits” and the flat areas are known as “lands.” These fluctuations are so tiny, you literally need a very strong electron microscope to view them:

Pits and lands on a discWhile the disc is spinning, a laser hits it and the light reflects from the disc either onto the optoelectronic sensor – when it hits a “pit” – or back onto the laser – when it hits a “land.” The disc drive assembly takes care of where the laser has to travel to hit its target. The pit represents a value of 1 and the land represents a value of 0. Sound familiar?

All those zeros and ones construct a file, and that concludes the “Optical Drives 101″ lesson. Congratulations!

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