Standards for CDs. CD rom

All standards for CDs are better known for the colors of the libraries in which they are described. In 1980, a series of standards called the Red Book relating to audio CDs was adopted. According to this document, the sampling rate when reading audio signals from a CD-ROM should be equal to 44.1 kHz. Amplitude resolution is represented by a 16-bit value. Since the standard defines stereo sound, then every second should be read not one, but two 16-bit values.

It is worth noting the main difference between audio CDs and CDs with digital data. It is clear that skipping (incorrect reading) of any depression on the disk surface can lead to loss of integrity of the recorded data. This in turn leads to the reproduction of incorrect information or the inability to launch executable modules of recorded programs.

Another thing audio CDs. Here, the omission of several pits on the disc has almost no effect on the sound quality. The fact is that in this case the principle of interpolation comes to the rescue. As it is known, interpolation allows finding the values ​​of intermediate values ​​by already known values. For example, suppose that three consecutive values ​​of 10, 13, and 20 were recorded on an audio disc. Suppose that the second number was not read for some reason (for example, due to dirty or damaged surface of the disc). Linear interpolation for the numbers 10 and 20 gives 15 [(10 + 20) / 2]. Of course, the obtained value does not coincide with the original one, which, however, in this case does not have special significance for encoding an analog signal (music), since the listening music will not sense it by ear.

The first standard called the Yellow Book for heterogeneous information CDs was adopted in 1985. This was one of the first steps towards the multimedia technology industry. According to this standard, all discs were divided into two categories: Mode1 and Mode2. Media belonging to the first category were recorded with error correction bits, while the transfer rate of useful information was 150 Kbytes / s. For disks of the second group, it was higher - 170 Kb / s - due to the lack of corrective bits.

Mode Mode2 in its original form has not been implemented. Audio and video information was stored in different parts of the disk, as a result of which the laser beam was forced to constantly “run” from one area of ​​the disk to another. Although the standard defined the error correction process used when reading data from a CD-ROM, it also did not provide sufficient specification regarding the structure of the stored file, which was more clearly defined by the ISO 9660 standard released in 1988.

The Green Book standard, adopted in 1986, is dedicated to CD-i interactive CDs (CD-interactive). It introduced the concept of headlines to simplify working with constantly intermittent video and audio information. In the Green Book standard, the idea of ​​constructing Mode2 was formally reworked. Mode2 compact discs were divided into two subgroups: Form1 and Form2. The first, as in the case of the Yellow Book category Mode1, defined the error correction process at the expense of additional bits and the information transfer rate of 150 Kb / s. The second subgroup allowed to have a read speed of 170 Kb / s due to the absence of error correction codes.

The XA (Extended architecture) standard was developed in 1990 jointly by Philips, Sony and Microsoft, and established compatibility criteria between CD-ROMs that meet the Green Book and Yellow Book standards. It determines the way of indexing multimedia information: graphics, text, raster images, sound. An XA-compliant disc can be played on an interactive Green-CD compatible CD-i reader, or by using a CD-ROM drive that conforms to the Yellow Book standard; supports XA operations and manages a special driver software.

Finally, in 1991, the Orange Book standard appeared, dedicated to CDs with the possibility of multiple recording.

Dynamic images and standard White Book.

The Standardization Expert Group (MPEG - Moving Picture Expert Group), has developed the MPEG-1 standard concerning the compression of full-format video (Full-Motion Video). It should be noted that this standard does not define the data storage format. The data in it can be played on a CD-i interactive disc reader, which is equipped with an MPEG decoder. Another option is to store MPEG-compressed full-format video on a CD-ROM device that complies with the Yellow Book standard.

The White Book standard, adopted in 1993, introduced some interactive features that allow you to quickly search for information on individual frames in direct access mode. The first White Book standard discs called Video-CD appeared in 1994. Currently, some Video-CD-type compact discs can be played on computers by unpacking according to the MPEG standard, if you install a card that hardwarely performs MPEG conversions. However, many CD-ROM drives do not read information in continuous mode, which makes it impossible to play these discs even after installing an MPEG card. In addition, the processor must be at least 386/25.

All compact discs for modern multimedia systems, including interactive compact discs CD-i and Video-CD, are recorded in the standard Mode2 / Form2, i.e. without the use of correction. The resulting gain in speed of 20 Kbytes / s is used to improve the quality of the video image. In this class of applications, the lack of error correction does not affect the quality, which cannot be said about business applications.

Photo CDs and multisessions.

One type of CD-ROM with the possibility of recording information is the so-called Photo CD. One-time recording of information on a disk is called a session. Accordingly, multiple recording is called multisession. It is necessary to take into account that each session requires its own table of contents, therefore, the greater the number of sessions used, the smaller the amount of information on the disk. Currently, disk drives that handle multisessions and allow you to play Photo CDs have already appeared.

Kodak has developed Photo CD devices that allow storing pictures taken on a 35 mm film in up to 100 frames. The idea is that the consumer could scan images obtained with the help of Kodak equipment, and later reproduce on any drive. In fact, five different versions of the same slide can be stored on a disk with a different resolution of the 24-bit palette.

With the help of compression (without loss of resolution) data of five images can be packaged into a file of 6 MB in size. Thus, a 600 MB compact disc can store up to 100 still images.

Fast drives are recommended for working with Photo CDs, because individual frames can reach sizes up to 18 MB.