What is an optical disc? The device of CDs, laser and other optical disks

A variety of data processing and storage facilities have densely entered our lives. In the distant past there were printed paper archives. What are modern media?

Optical disc: history of creation

The first device for storing audio recordings was produced by Sony in 1979. It represented itself, as now, a plastic disk with a round hole in the center. Initially it was used only for recording audio files, and information on it was applied using a special method of encoding Pulse Code Modulation. It consists in the fact that the text or sound passes through the analog-to-digital converter and turns into a set of bits.

Later, in 1982, mass production of disks began in Germany. They began to buy to store a variety of files. Soon they were on the counters of not only music stores.

How does the CD work? To make the base, use a 1,2-mm thick polycarbonate plate with a diameter of 120 mm, which is first covered with a thin layer of metal (gold, aluminum, silver, etc.), and then lacquer. It is on the metal is applied information in the form of pits (depressions), squeezed out along a spiral path. Reading files recorded on an optical disc, Occurs by means of a laser beam with a wavelength of 780 nm. It is reflected from the surface of the plate, it changes the phase and intensity, falling on the pits. Land is also called gaps between pits. The pitch of one track in the spiral is about 1.6 μm.

Types of optical disks

There are several types of CDs: Compact Disc (CD), Digital Versatile Disc (DVD), Blu-ray Disc (BD). All of them have different capacities for recording information. For example, DVDs are produced in capacities from 4.3 to 15.9 GB, and CDs - only up to 900 MB.

Also discs are distinguished by the multiplicity of the record: single and multiple. In such carriers, the relief structure of pits is formed in different ways. Overwritting is possible thanks to the organic material, which under the influence of the laser darkens and changes the reflection coefficient. In common parlance, this process is called a burn.

More optical media can differ in form. Shaped CDs (Shaped CDs) are usually used in show business as audio and video file keepers. They are of arbitrary shape (square, in the form of an airplane or a heart). It is not recommended to use them in CD-ROM drives, because they can burst at high speeds.

CD-ROM drives and their types

The CD-R optical disc is a carrier of information that is read-only. You can write files to it only once without the right to add and edit. Initially, the capacity of such drives reached only 650 MB or 74 minutes of audio recording. Now devices are available that can hold up to 900 MB of information. Their advantages are that reading supports all standard CDs.

The same amount of memory has a laser disc CD-RW, only files on it can be recorded many times (up to 1000 times). For this, standard computer programs are used. The downside is that not all devices are ready to work with this format. Standing CD-RW is slightly more expensive than CD-R.

CDs with audio and video recordings do not possess any degree of protection, they can be copied and reproduced. But carriers with certain data are protected from copying with StarForce technology.

ROM format discs are recorded in the factory and are only capable of reproducing data. It is not possible to edit such a medium. But optical devices such as RAM can be rewritten up to 10 thousand times and they serve up to 30 years. Such disks are produced in additional cartridges, their reading is not supported by conventional disk drives.

DVD-players and their characteristics

The Digital Versatile Disc is a digital multipurpose media. Its structure is more dense and holds a lot of information (up to 15 GB). Such an optical disk resembles two CDs glued together. Storage and reading of a large amount of information is possible due to the use of a red laser whose wavelength is 650 nm, and lenses with a maximum numerical aperture. DVDs have one or two recording sides, as well as one or two working layers on each side. These indicators determine their capacity.

Like CDs, DVDs are divided into several formats. DVD-R or DVD + R are media on which you can only record information once. The standard recording on these discs was developed by Pioneer in 1997. "Minus" and "plus" devices differ material reflective layer and special markings.

Optical DVD RW (DVD + RW, DVD-RW) have the ability to repeatedly rewrite information. And the "plus" media allows you to make changes to the places you need. Universal drives help solve the incompatibility of formats (+ RW and -RW).

What is Blu-ray Disc?

This type of optical disc allows you to store and record digital data at high density. To reproduce information (even high-definition video), a 405-nm blue laser beam is used, which narrows the spiral path twice. Files that are very close to each other are susceptible to mechanical damage, so the disc should be specially treated. Recently, carriers with a special coating are produced, which can be wiped with a normal dry cloth.

There are disks Blu-ray disposable and reusable recording, as well as multi-layer (from 2 to 4 layers). The capacity of the most "layered" media reaches 128 GB. In this case, it has a standard 12-centimeter diameter. A two-layer standard Blu-ray disc can hold up to 50 GB of information. In development is a device that reaches a capacity of 300-400 GB, which can read modern disk drives. For camcorders smaller diameter disks (80 mm) are used with a memory capacity of up to 15 GB.

For protection against copying Blu-ray are equipped with digital watermarks ROM-Mark and technology Mandatory Managed Copy.

The purpose of MiniDVD-carriers

Optical Mini DVD media is a small copy of the usual Digital Versatile Disc. It is 8 cm in diameter and is used in photo and video cameras. Single-sided disk holds up to 1.4 GB of information, respectively, two-way - 2.8 GB. In the format they are MiniDVD-R (single write) and MiniDVD-RW (multiple).

The standard 12-inch drive is not designed for reading a Mini DVD. When using these discs in the laptop, use the drive motor spindle. Sometimes there are problems with reading the information carrier. Typically, in such cases, the computer displays the words "the driver for the optical drive is not found". To solve the problem, you should contact an experienced programmer.