How do players and computers read CD’s and DVD’s?

99 views
0

I’m just wondering physically how is it possible? Why is it that if I wanna pick one song from the CD the player ‘knows’ where the song I want is?

In: Technology

Little tiny reflective/non reflective dots represent 1’s and 0’s

The drives laser shoots at the disc and it being bounced back/not bounces back gets turned into binary

The backside of the label is made of a reflective coating, so that when light is shone through the plastic of the disc it is reflected back out. A laser shines upwards through the disc.

In the plastic of the disc there are microscopic dimples or *pits* that change how the laser light is reflected. Specifically, they cause the waves of light to overlap in a way that causes destructive interference, which means no light reaches the detector next to the laser emitter.

So either there’s a pit, or a land. Light enters the detector, or it doesn’t. The 1s and 0s of binary are encoded in the pits and lands. It is *not* that a pit or land is a 1 and the other is 0. Instead, a 1 is when the laser detects a *change* from land to pit or vice versa.

The laser follows tracks, like the grooves in a record. A chip precisely controls the position of the laser, so the player knows exactly where on the disc the reader is. That means it also knows precisely how fast the disc is turning. It uses that to calculate the clock rate, or how fast 1s and 0s should be happening.

DVDs use a more precisely controlled reader and more sensitive reader so the pits can be smaller and closer together, which means more data can be packed onto the disc. The format of the data is also different.

Blue ray players use a blue laser, which has a smaller wavelength. That means it can read smaller pits, so they can be even smaller than in DVDs and pack in more data. Blue ray players and HD-DVDs both have multiple layers, too. The laser has a lens to change the focus to ignore or pick up different layers.

Nobody answering the question OP asked.

A CD, or any optical media is made up of a continuous spiral of 1s and 0s represented as reflective flats, and non reflective pits.

At the beginning of the disk is a table of contents of sorts. It tells the system where physically on the media a particular file is. It basically tells the drive that file x starts at sector 423. The drive knows roughly where the laser is physically on the disk, so in order to “seek” to a particular file, it can move the laser and count how many tracks of the spiral it passes over. Once it’s close, it slows down and reads the whole spiral searching for the start of the file. Once the start is found, the data begins to stream from the drive out to the system. From there the file can be played or loaded into memory wholesale and worked on locally.

Answer : this actually blows my mind also
You thought CD backside is smooth, but it is not. The fact is they are filled with little bumps. Troff and groves acts like 1 and 0 basically binary.
CD reader shines laser into the bumps, the light reflected indicated whether the spot is actually 0 or 1.
All of this is happening within nano seconds