What is cd dvd rom. Parameters of CD-ROM drives. Burning a CD-R disc in multiple sessions

4. CD/DVD-ROM drive

These days, the CD/DVD-ROM drive is an integral part of the computer, as almost all software is now distributed on CDs, and individual multimedia programs are on DVD. DVD drives support both regular CDs and DVDs, making them more versatile. Modern systems have long had the ability to boot from CD-ROM/DVD-ROM drives.

To achieve the desired effect when using a CD-ROM, it is recommended to choose a drive with an EIDE interface of at least 32x or 40x, or a DVD-ROM with a speed of 8x.

I would recommend purchasing both CD-RW and DVD-ROM. They're not the cheapest devices yet, but once you get them, you'll immediately experience the benefits of using them: burning your own CDs, 4.7-17 GB of data to DVD, and more. Another reason to install a CD-RW drive and a CD-ROM/DVD drive at the same time is that you can save the contents of an optical disc without having to copy it to HDD.

Burning your own CDs will help you save your data with a minimum of effort. CD-RW drives are used to write both CD-RW (write-once) and CD-R (write-once) media. Note that many older CD-ROM drives (without the MulliRead label) do not support CD-RW discs, while almost all CD-ROM drives are compatible with the CD-R standard.

Advice. For maximum recording reliability CD-R discs W needs one of the technologies by which buffer overflows can be prevented. BURN-proof, JustLink or Waste-Proof are such technologies that eliminate the possibility of incorrect recording (and, therefore, damage) of discs.

5. Keyboard and mouse

Obviously, the computer will need a keyboard and a cursor positioning device, such as a mouse. The choice of a specific modification of these devices directly depends on the personal preferences of the user. Different users like different types of keyboards, so you will have to try a lot of models before you find the one that suits you best. Some people like keyboards with springy keys that can be "feeled" while others prefer "soft" keyboards that allow easy keystrokes.

There are two types of keyboard connectors, so please make sure that the keyboard connector matches the connector installed on the motherboard when purchasing. The original 5-pin DIN connectors and the newer 6-pin mini-DIN connectors are electrically compatible, allowing you to adapt one type of keyboard connector or another to your existing keyboard. The most modern keyboard interface is the USB bus; USB connectors have become the most widely used, not least due to "legacy-free" computers containing only USB ports.

When using a USB keyboard, like any other device of this type, USB support is required at the Basic Input/Output System (BIOS) level. If you want to use the USB keyboard outside of the graphical user interface Windows interface, then the system BIOS must support a technology called Legacy USB or USB Keyboard and Mouse. This feature is supported by almost all modern BIOSes. In the meantime, try to find a model that also works with traditional keyboard ports so that you can use a USB keyboard on both newer and older systems.

The same applies to other cursor positioning devices (such as a mouse). Everyone can choose the most suitable option among a wide variety of modifications. Before finally deciding what to buy, try several options. If your motherboard has a built-in mouse port, make sure the connector you choose matches it. A mouse with this connector is commonly referred to as a PS/2 mouse because this type of mouse port was first used on IBM's PS/2 systems. Many computers use a serial port to connect a mouse, but if you can use the mouse port built into the motherboard, it's better to use it. Some USB mice work with the PS "2 port without any problems, but mostly mice of this type are only for the USB port. I think the most acceptable option is a dual-mode mouse that works on any system. Do not forget about the existence of wireless versions of the mouse.

Tip: Don't skimp on the keyboard and mouse! An "uncomfortable" keyboard and mouse can cause illness! Personally, I recommend high quality keyboards with capacitive sensors.

The Universal Serial Bus (USB) is gradually replacing all other standard I/O ports. The USB interface supports PnP technology and allows you to connect up to 127 external devices to one port, and the data transfer rate of the USB bus is about 60 MB / s. As a rule, a USB hub is connected to the USB port integrated into the system board, and all devices are connected directly to it. At the moment, USB ports are present in almost all motherboards.

The range of devices connected to USB is unusually wide. These include modems, keyboards, mice, CD-ROM drives, acoustic systems, joysticks, tape drives and floppy drives, scanners, camcorders, MP3 players and many others. However, if you connect multiple devices to the same low-speed USB port 1.1, there may be some issues that need to be upgraded to USB 2.0. When buying a new system, pay special attention to the availability of USB 2.0 ports.

Batch mode, which allows you to perform a whole series of tests without operator intervention. You can create an automated diagnostic program that is most effective if you need to identify possible defects or run the same sequence of tests on multiple computers. These programs check all types of system memory: basic (base), extended (expanded) and...

Various possibilities. Such a division of the PC could thoroughly confuse not only ordinary users, but also technical support specialists. However, even such a classification is still better than none. Today, there are five classes of computers, with mobiles in a separate group: the requirements for such devices are very specific. The division into categories will allow ...

... (Wide Area Information Server) server; news - Usenet newsgroup; telnet - access to Telnet network resources; ftp is a file on an FTP server. host. domain - domain name on the Internet. port is a number to specify if the method requires a port number. Example: http://support. vrn.ru/archive/index.html. The http:// prefix indicates that the web page address follows, / ...

N OS-6). It should be noted that the replacement of computer parts is unprofitable to consider as an upgrade. For an accountant, this is a lot of work. By the amount of modernization in accounting, you need to increase the initial cost of the computer. This means that the cost of modernization will not have to be written off immediately, but gradually, as depreciation is accrued. Therefore, in practice, upgrading a computer, if possible ...

Meet in our time a computer without CD-ROM/DVD drive almost impossible. CDs and DVDs contain a wide variety of programs, music, documents, digital photos, and more. You can purchase both discs with already recorded data (for example, a music CD or DVD with a movie), or special discs on which you can (once or several times, depending on the disc and drive) burn any information you need.

In addition to the not entirely correct name " drive”, CD/DVD readers and writers are also referred to as optical drives. Word storage device generally refers to all devices designed to store or read data. For example, HDD can be called a disk drive. The word "optical" refers to the method of reading data from discs. In CD / DVD drives, reading and writing data from discs is carried out using a special laser beam.

There are several types in total CD-ROM and DVD drives, with and without write support. Let's consider them in more detail.

Regular disk drive CD— ROM allows only read data from disks CD, CD— R and CD— RW. You cannot write data to any discs with it. Such drives are the cheapest, but they are already outdated and are not installed in new computers.
Drive CD— ROM with recording capability. Unlike the previous version, with the help of such a drive, you can write data to disks with a single (CD-R) or multiple (CD-RW) recording.
Drive DVD. This drive combines the capabilities of the two previous drives, i.e. allows you to write and read data from CDs, and can also read data from DVDs.
Drive DVD with recording capability. This is the most versatile and popular drive option and is recommended for purchase. With this drive, you can read and write any discs, including CD, CD-R, CD-RW, DVD+-R/RW.
Also, Blu-ray disc drives are becoming more and more popular every year.

Main types of optical discs

As you already understood, the recording capabilities depend not only on the drive, but also on the discs themselves. Let's study the main types of optical discs that currently exist.

CD, or CD. The simplest version of the optical disc. On such discs, either music (music CDs) or various programs are sold. Nothing can be written to such a disc.
CD-R disc. Such a disk can once write down the information you need. You can't add it later. A single CD-R disc can store up to 880 MB of data, depending on the size of the disc. These disks are most often used for storing important information which will not need to be changed in the future. It can be music, video files, etc.
CD-RW disc. This disc has the same capacity as CD-R discs, but you can write data to it many times and delete data you don't need. In total, such a disk is designed for approximately 1000 rewriting cycles, which is more than enough, for example, for periodic recording. Word documents, their subsequent deletion and recording of new files. CD-RW discs are more expensive than CD-R discs.
Diskdvd-rom,orDVD video. DVDs are sold on these discs. Nothing can be written to such a disc. At the same time, the volume of a single-layer DVD disc is 4.7 GB, which is several times larger than the volume of CD discs.
DiskDVD— Rand diskDVD+ R. Just like CD-R discs, DVD-R discs and DVD+R one write down the data you need. Unfortunately, at one time, companies - manufacturers of optical discs and drives took up arms against each other and became irreconcilable enemies, as a result of which two completely incompatible standards appeared, DVD+R and DVD-R. Fortunately, manufacturers of optical drives have solved this problem and now for most drives it does not matter at all which disc to take; Both types of drives will be supported.
DiskDVD+ RWandDVD— RW. Similar to CD-RW discs, DVD+RW and DVD-RW discs can be written to multiple times With a disc capacity of 4.7 GB, it is very convenient for storing and backing up a wide variety of data such as your music collection, etc. . The problem of standards incompatibility exists here as well, and it is solved in the same way - by the release of universal small format drives that support any type of disc.
Diskblue— rey we have a huge volume that allows you to record up to 80 gigabytes of information! Agree this is a lot for an optical drive! In most cases, I record video with increased clarity on such discs, which allows you to achieve the maximum quality of the movie! The cost of such a drive can reach up to 2000 rubles!

Optical drive speed

The speed of an optical drive is usually indicated in this way 52x/24x/52x. This means that CD-R discs are recorded from 52x, recording discs CD-RW happening at a speed 24x, and reading CD-R/RW discs - also at 52x speed. In this case, the indicator 1x means a data transfer rate equal to 153 Kb / s. Now let's calculate the speed of the drive with a reading speed of 52 x. To do this, multiply 52 by 153, the result will be 7956 KB / s, i.e. almost 8 MB/s.

Compared to CD-ROM drives, rewritable DVD drives read and write data much faster. The 1x speed of a DVD-ROM drive is 1.35 MB/s, which is the same as 9x speed for a CD-ROM. Therefore, the speed of modern DVD-ROM drives with a read speed of 20x corresponds to the speed of 180x for CD-ROM drives (27 MB / s), although, of course, such a speed does not exist for CD-ROM drives.

Any hardware or software part of a computer uses a processor. Processor utilization refers to the amount of time that the processor spends performing a specific task. Low CPU usage during a task indicates that other devices and programs will get access to it faster. For CD/DVD-ROM drives, there are three factors that affect CPU usage: drive speed CAV, buffer size, and interface type.

Direct memory access

Currently, almost all computers have a controller installed. Bus Master IDE, which allows you to put data directly into RAM, bypassing the processor. When using such controllers, the processor load by a CD/DVD-ROM drive (regardless of the type of interface) is reduced to 11%.

Virtually all modern CD-ROM drives (12x and above) and motherboards support direct-to-memory transfers. To determine if your system supports DMA, click the icon System in the window Control Panel. In the tab Devices (Device Manager) click on the "+" sign next to the device group Hard Disk Controllers. If there is a device in the list bus master, then your system supports direct memory access. It is not enough to have a controller to set up direct memory access Bus Master IDE, we need more devices (hard drives and CD-ROM drives) that will support this mode. Find out the type of drives installed in your system and consult manufacturers for supported features. Hard drives and CD-ROM drives that support modes MultiWord DMA Mode 2 (16.6 MB/s), UltraDMA Mode 2 (33 MB/s), UltraDMA Mode 4 (66 MB/s) or faster may use direct memory access.

To enable direct memory access hard drive or CD-ROM drive, double click on it in the tab Devices dialog box Properties: System and in the appeared window of properties of this device in the tab Settings) check the box DMA.

Interface

Under interface CD-ROM drive refers to the physical connection of the drive to the expansion bus. Since the interface is the channel through which data is transferred from the drive to the computer, its importance is extremely high. The following types of interfaces are used to connect a CD-ROM drive to a computer:

SCSI/ ASPI (Small Computer System Interface/Advanced SCSI Programming Interface) ;
IDE/AT API (Integrated Device Electronics/AT Attachment Packet Interface) ;
parallel port;
USB port;
Fire Wire (IEEE-1394).

Loading mechanism

There are three fundamentally different types of loading CDs: drive containers, drawers, and autoloaders.

Drawers

Most simple CD drives use drawers. In order to replace a disk, you need to slide the tray out of the drive, remove the disk, put it in a transparent plastic box, remove a new disk from another identical box, put it in the tray and slide it back.

Containers

At one time, this disc loading mechanism was used in most high-quality CD drives, as well as in CD-R and DVD-RAM. The disk is installed in a special, tightly closed container with a movable metal flap. It has a lid that is flipped open solely to place the disc in or out of the container; the rest of the time the lid remains closed. When the container is placed in the drive, the metal shutter is moved to the side by a special mechanism, opening the way for the laser beam to the surface of the CD.

Autoload mechanism

Some drive models use an autoload mechanism, i.e. you put a CD in the slot on the front panel, and the autoload mechanism "sucks" it in on its own. However, this mechanism does not allow the use of 80 mm discs or other discs with modified physical formats or shapes.

Other Features of CD Drives

Of course, the advantages of devices are primarily determined by their technical specifications but there are other important factors as well.

In addition to the quality of construction and reliability, when choosing a drive, it is necessary to take into account its following properties:

dust protection;
automatic lens cleaning;
drive type (external or internal).

Automatic lens cleaning

If the lenses of the laser device are dirty, reading data is slowed down because it takes a lot of time to repeat the search and read operations (in the worst case, data may not be read at all). In such a situation, special cleaning discs should be used. Some modern, high-quality drives have a built-in lens cleaner.

CD burners

There are two main types of recordable CDs and drives: recordable CD-R (Recordable) and rewritable CD-RW (Rewritable).

Most CD-ROM writers are devices WORM(write once, read many - one-time write, multiple reading), intended for long-term storage. CD-R drives have become the de facto standard for this type of device. They are ideal for system backups and similar operations. However, with frequent backup or archiving, despite the low cost of the media, it becomes unprofitable to use CD-R devices. In this case, you should pay attention to multiple recorders CD-RW.

CD-R drives

CD-R discs that have some data already written on them can be played or read by almost any standard CD-ROM drive. This type of disc is very useful for storing archival data and creating master discs that can be replicated and distributed to employees of small companies.

CD-R discs operate on the same principles as standard CD-ROMs, reflecting a laser beam off the surface of the disc and following changes in reflectance as trough-to-trough or trough-to-trough transitions occur. On conventional CDs, the spiral track is extruded or stamped into the polycarbonate mass. CD-R discs, on the other hand, have a pit pattern burned into the raised spiral track. Thus, depressions are dark (scorched) areas that reflect less light. In general, the reflectivity of the pits and lands remains the same as that of pressed discs, so conventional CD-ROM drives and music CD players read both pressed discs and CD-Rs.

The CD-R recording begins even before you insert the disc into the drive. The manufacturing process for CD-R media and standard CDs is almost the same. In both cases, the melted polycarbonate mass is pressed using a shaping matrix. But instead of stamping cavities and platforms, the die forms a spiral groove on the disk (called initial groove (pre)groove)). When viewed from the side of the read (and write) laser located under the disk, this groove is a helical protrusion, not a depression.

The boundaries of the spiral protrusion (original groove) have certain deviations from the longitudinal axis (the so-called fluctuations). The oscillation amplitude with respect to the distance between the turns of the track is quite small. The distance between the turns is 1.6 microns, and the amount of transverse deflection of the protrusion reaches only 0.03 microns. The fluctuations of the CD-R groove modulate some additional information that is read by the drive. The sync signal, determined by the jitter of the track, is modulated along with the time code and other data and is called the absolute time of the original track ( Absolute Time In Pre-groove-ATIP). The time code is expressed in the format "minutes: seconds: frame" and is included in the Q-subcodes of the frames recorded on the disc. The ATIP signal allows the drive to allocate the necessary areas on the disk before actually recording frames. Technically, the position signal is a frequency drift and is defined by a carrier frequency of 22.05 kHz and a deviation of 1 kHz. Changes in the oscillation frequency are used to transmit information.

The CD-R manufacturing process is completed by spin-coating a uniform layer of organic dye. Then a golden reflective layer is created. The surface of the disc is then coated with a UV-cured acrylic lacquer, which is used to protect the previously created gold and painted layers of the disc. Studies have shown that aluminum used with an organic dye is susceptible to severe oxidation. Therefore, CD-R discs use gold plating, which is highly resistant to corrosion and has the highest possible reflectivity. A layer of paint is applied to the surface of the disc, covered with a layer of varnish, using a screen printing method, which is used to identify and additionally protect the disc. The laser beam used to read and write the disc first passes through a transparent polycarbonate layer, an organic dye layer, and, reflected from the gold layer, again passes through the dye layer and polycarbonate mass, after which it is captured by the optical sensor of the drive.

The reflective layer and the organic dye layer have the same optical properties as unallocated compact disc. In other words, a track of an unrecorded (blank) CD-R disc is perceived by the CD reader as one long area. The laser beam of a CD-R drive has the same wavelength (780 nm), but the power of the laser used for recording, in particular for heating the colored layer, is 10 times higher. The pulsed laser heats the organic dye layer to a temperature of 482-572°F (250-300°C). At this temperature, the dye layer literally burns out and becomes opaque. As a result, the laser beam does not reach the gold layer and is not reflected back, which achieves the same effect as when canceling the reflected laser signal that occurs when reading stamped CDs.

While reading a disc, the drive reads non-existent pits, which are areas of low reflectivity. These areas appear when the organic dye is heated, so the process of writing a disc is often called burning. The burnt areas of the dye change their optical properties and become non-reflective. These properties can only be changed once, which is why CD-Rs are called write-once media.

Drives CD-RW backwards compatible with CD-R devices and allow data to be read from or written to CD-R media.

CD-RW is characterized by the following:

they can be overwritten;
have a higher cost;
are characterized by a lower write speed;
have lower reflectivity.

In addition to high cost and the ability to overwrite data, storage media CD-RW also differ in lower (two or more times) recording speed. This is because the laser takes longer to process each region of the disc when it is written. Disks CD-RW also have lower reflectivity, which limits their readability. carriers CD-RW, for example, are not readable by many standard CD-ROM and CD-R drives. Therefore, CD-R discs are better for burning music discs or compatibility with different types of drives. It should be noted that MultiRead technology, currently supported by almost all drives with a speed of 24x and higher, allows you to read discs CD-RW without any problems. The presence of this feature is determined by the MultiRead logo printed on the case of the CD-ROM drive.

Drives and CD-RW media use a state phase change process to create the appearance of depressions on the surface of a disc. The discs are created on a polycarbonate substrate containing a pre-formed, wavy-shaped helical groove whose vibrations determine the positioning information. The upper part of the base is covered with a special dielectric layer (insulation), after which a recording layer, another dielectric layer and an aluminum reflective layer are applied. The surface of the disc is then coated with a UV curing acrylic lacquer that is used to protect the previously created layers of the disc. The dielectric layers above and below the recording layer are designed to shield the polycarbonate substrate and the reflective metal layer from the intense heat used during the phase change recording process.

CD-R discs are written by heating certain areas of the organic dye (ie the recording layer). In turn, the recording layer CD-RW is an alloy of silver, indium, antimony and tellurium (Ag-In-Sb-Te), which has the possibility of phase transformations. An aluminum alloy is used as the reflective part of the recording layer, which is no different from that used in conventional stamped discs. During the operation of reading or writing data, the laser device is located on the underside of the disc. When viewed from the side of the laser, the spiral groove will look like a protrusion, and the recording layer of the disc will be located on its upper plane.

The Ag-In-Sb-Te alloy used as the recording layer has a polycrystalline structure with a reflectivity of 20%. While writing data to disk CD-RW the laser can operate in two modes, which are called P-write and P-erase. In P-write mode, the laser beam heats the material of the recording layer to a temperature of 500-700 °C (932-1229 °F), which causes it to melt. In the liquid state, the alloy molecules begin to move freely, as a result of which the material loses its crystalline structure and becomes amorphous(chaotic) state. The reflectivity of the material frozen in the amorphous state is reduced to 5%. When reading a disc, areas with different optical properties are perceived in the same way as the depressions of a conventional stamped CD-ROM disc.

In the erase mode, the layer of active material is heated to approximately 200°C (392°F), which is well below the melting point, but sufficient to soften the material. When the active layer is heated to the specified temperature, followed by slow cooling, the structure of the material is transformed at the molecular level, i.e. transition from amorphous to crystalline state. In this case, the reflectivity of the material increases up to 20%. Areas having a higher reflectivity perform the same function as the zones of a stamped CD.

Although this mode of laser operation is called P-erase, data is not directly erased. Instead, technology is used direct data overwriting, when using which the sections CD-RW, which have a lower reflectivity, are not erased, but simply overwritten. In other words, during data recording, the laser is constantly on and generates pulses of varying power, thereby creating regions of amorphous and polycrystalline structures with different optical properties.

Drive Compatibility: MultiRead Specifications

To indicate the compatibility of a particular drive, the OSTA (Optical Storage Technology Association) has developed an industry standard, testing system and logo, which should guarantee certain levels of compatibility. All of this is called the MultiRead specifications. The following specification levels currently exist:

MultiRead for CD-ROM drives;
MultiRead2 for DVD-ROM drives.

In addition, a similar standard has been developed MultiPlay, which is intended for device owners DVD video and CD-DA.

MultiRead and MultiRead2 standards for CD/DVD drives

Carrier	MultiRead	MultiRead2
CD-DA (Digital Audio)	x	x
CD-ROM	x	x
CD-R	x	x
CD-RW	x	x
DVD-ROM	-	x
DVD video	-	x
DVD Audio	-	x
DVD-RAM	-	x

x - the drive will read from this media.

The presence of one of these logos guarantees the appropriate level of compatibility. If you are purchasing a CD-ROM or DVD drive and want to read rewritable or writable discs, make sure the drive has the MultiRead logo on it. For DVD drives, the MultiRead version will be much more expensive due to the additional cost of the dual laser mechanisms. Almost all DVD-ROM drives used in computer systems, have a dual reading mechanism, which allows you to read data from CD-R discs and CD-RW.

Shape CD (figured compact disc) - an optical carrier of digital information of the CD-ROM type, but not strictly round in shape, but with an outline of the outer contour in the form of various objects, such as silhouettes, cars, planes, hearts, stars, ovals, in the form credit cards, etc.

Usually used in show business as a carrier of audio and video information. The record was patented by producer Mario Koss in Germany (1995). Usually, discs with a shape other than round are not recommended for use in computer CD-ROM drives, since at high rotation speeds the disc may burst, which can lead to a complete failure of the drive.

Rewritable and DVD Standards

DVD drive and media compatibility

Drives	CD-ROM	CD-R	CD-RW	DVD video	DVD-ROM	DVD-R	DVD-RAM	DVD-RW	DVD+RW	DVD+R
DVD-Video player	R	?	?	R	-	R	?	R	R	R
DVD-ROM drive	R	R	R	R	R	R	?	R	R	R
DVD-R drive	R	R/W	R/W	R	R	R/W	-		R	R
DVD-RAM drive	R	R	R	R	R	R	R/W	R	R	R
DVD-RW drive	R	R/W	R/W	R	R	R/W	-	R/W	R	R
DVD+R/RW drive	R	R/W	R/W	R	R	R	R	R	R/W	R/W
dvd-multi drive	R	R/W	R/W	R	R	R	R/W	R/W	R	R
DVD+/-R/RW drive	R	R/W	R/W	R	R	R/W	R	R/W	R/W	R/W

The history of rewritables and DVDs began in April 1997 when companies in the DVD Forum group introduced specifications for rewritable DVDs.

DVD-ROM drive(DVD-ROM drive (DVD-ROM drive, DVD-R / RW drive) - a computer device designed to read high-density optical discs (DVD), as well as play audio, video and CDs. Writer models DVD-RW drives, which by 2006 began to dominate the market, can not only read, but also write / rewrite discs of various formats (DVD and CD).

Data is read/written to DVD in the same way as regular CDs (see CD-ROM drive), but DVD drives use a reduced laser beam (to 0.63-0.65 µm vs. 0.78 µm). in CD-ROM) of a long wavelength, which makes it possible to distinguish smaller pits (0.4 μm versus 0.83 μm in CD-ROM), which, together with a decrease in the distance between the turns of the track and other technological features, significantly increases the recording density on the disc. In addition, the use of a narrower laser beam in DVD drives led to a reduction in the protective layer of the disc by half, which made it possible to create double-layer DVD discs (DB, double layer) and further double the storage capacity. Modern DVD drives are able to change the focus of the laser beam, allowing data to be read from the layers of a single-sided disc located one under the other. To read/write double-sided discs, drives with two independent laser heads can be used. Modern drives are capable of changing the wavelength and radiation power to read / write various formats of compact discs (DVD and CD). Like CD-ROM drives, DVD drives differ in data transfer speed, access speed, buffer capacity, support for certain disc formats (including DVD-R/RW, DVD+R/RW, CD-R/RW) and recording methods, as well as other characteristics.

DVD read/write speeds are indicated by a multiplier (x1, x2, etc.) similar to the corresponding CD-ROM speeds, however, the unit of speed here is not 150 Kb/s, but 1.321 Mb/s (video reading speed). ). For DVD movie playback, the maximum possible read speed is not important, since all movies play at the same speed, but the speed of the drive may be important when writing/reading data.

The mass production of these drives began at the end of 1996, but their widespread introduction was delayed for more than a year. This was due, in particular, to the fact that the first versions of the drives did not allow playing regular CD-ROMs. In addition, DVD-ROM recordings had not yet been mass-produced and users did not yet have a sufficient number of recordings. Nevertheless, it was already initially assumed that DVD-drives and discs should, within a relatively short period of time, force out the corresponding products of CD-ROM technology from the market. The beginning of the active production and distribution of drives and disks of this type can be attributed to approximately the second half of 1997. The greatest activity in the use of the new media was shown by American manufacturers of film products and game programs.

At the end of 1997, the second generation technology (DVD-2) appeared. Products based on this technology overcome a number of shortcomings of earlier releases of devices that cannot read CD-R and CD-RW media, which are becoming increasingly popular as their prices drop. In addition, these drives are faster than DVD-1 drives. By the beginning of 1998, a significant number of games and films in MPEG-2 format were released on these media.

When, in the early 1980s, Sony and Philips released sound CDs(Compact Disc - CD), no one could have imagined what a valuable storage medium they would become in the near future. The durability, random accessibility, and high sound quality of CDs brought them worldwide attention and contributed to their widespread adoption. The first CD-ROM drive (CD-ROM drive) for PCs was released in 1984, but it took several years before it became an almost indispensable component of high-quality PCs. Now games, software applications, encyclopedias and other multimedia programs are distributed on the CD-ROM (figuratively speaking, now "from an expensive luxury, the CD-ROM drive has turned into a cheap necessity"). Actually, the "multimedia revolution" owes a lot to cheap high-capacity CD-ROMs. If an audio CD was designed to play 74 minutes of high-quality digital audio, a computer CD-ROM can store 660 MB of data, over 100 top-quality photographs, or a 74-minute TV movie. Many discs store all these kinds of information, as well as other information.

CD-ROM drives play an important role in the following aspects of a computing system:

Support software : The most important reason that the modern PC must having a CD-ROM drive is a huge number of software applications distributed on CDs. Now floppy disks are practically not used for this.
Performance A: Since many programs now use the CD-ROM drive, the performance of the drive is important. Of course, it is not as critical as the performance of the hard drive and PC components such as the processor and system memory, but it is still important.

Thanks to mass production, modern CD-ROM drives are faster and cheaper than before. The vast majority of software applications are now distributed on CD-ROM, and many programs (such as databases, multimedia applications, games, and movies) can be run directly from CD-ROM, often over a network. The modern CD-ROM drive market offers internal, external and portable devices, single and multi-disk auto-changers, SCSI and EIDE drives, and a variety of standards.

Most CD-ROM drives have convenient controls on the front panel that allow you to use the drive to play and listen to audio CDs. Usually there are such controls:

Stereo headphone output: A small socket (jack - jack) for connecting headphones and listening to an audio CD.
Rotary knob for volume control: To adjust the audio output volume.
Start and Stop buttons: For starting and stopping audio CD playback. On some drives, these buttons are the only controls.
Next Track and Previous Track buttons: These buttons allow you to skip to the next track and previous track of an audio CD.

CD-ROM drives were introduced after PC drive bays were standardized, so they fit a standard 5.25" drive bay. The height of a CD-ROM drive is 1.75", which is the standard "half-height" drive bay. Most drives have a metal casing that has holes for mounting screws, making it easy to mount the drive in the bay. To install the disc is usually used retractable tray (tray).

Structure of a CD-ROM

A CD-ROM drive can be compared to a floppy disk drive because both drives use removable(removable) media. It can also be compared to a hard disk drive, as both drives have a large capacity. However, a CD-ROM is neither a floppy disk nor a hard disk. If floppy and hard disk drives use magnetic(magnetic) media, then the CD-ROM uses optic(optic) carrier. The base CD-ROM is 120 mm (4.6") in diameter and is a kind of 1.2 mm thick "sandwich" of three coatings: a back layer of transparent polycarbonate plastic, a thin aluminum film and a varnish coating to protect the disc from external scratches and dust.

In a traditional manufacturing process, millions of tiny cavities, called pitami(pits), on a spiral that unfolds outward from the center of the disc. The pits are then coated with a thin aluminum film that gives the disc its characteristic silver color. A typical pit is 0.5 µm wide, 0.83 to 3 µm long, and 0.15 µm deep. Distance between tracks ( track pitch- pitch) is only 1.6 µm. The track density is over 16,000 tracks per inch (Tracks Per Inch - TPI); for comparison, a floppy disk has a TPI of 96 and a hard disk has a TPI of 400. The length of the unfolded and extended spiral is about four miles.

Of course, CDs must be handled with care. The working side of the disc is the most sensitive to damage. Despite the fact that the aluminum layer is protected from damage and corrosion by a varnish coating, the thickness of this protective layer is only 0.002 mm. Rough handling or dust can cause small scratches and tiny cracks through which air enters and oxidizes the aluminum coating, rendering the disc inoperable.

How a CD-ROM Drive Works

Except for some very sophisticated error checking, the operation of a CD-ROM drive is very similar to that of an audio CD player. The data is stored in the same way as on all CDs. Information is stored in 2 KB sectors on a spiral track that starts at the center of the disk and "unrolls" towards the outer edge of the disk. Sectors can be read independently.

The player reads information from pits and lands(lands) of a CD spiral track starting from the center of the disc and moving towards the outer edge. For reading, an infrared laser beam with a wavelength of 780 nm is used, which generates a low-power gallium arsenide semiconductor. The beam passes through the transparent coating layer onto the metal film. Although the laser is low power, it can damage the retina if it enters the unprotected eye. When the disk rotates at a speed of 200 to 500 revolutions per minute (Rotations Per Minute - RPM), the beam is reflected from the pits and the frequency of the light changes.

Areas around the pits, called lands are also involved in the reading process. Reflected light passes through a prism to a photosensor whose output is proportional to the amount of light received. The light reflected from the pits is out of phase by 180 degrees from the light reflected from the lands, and the differences in intensity are measured by photovoltaic cells and converted into electrical pulses. As a result, a sequence of pits and lands of variable length, stamped on the surface of the disc, is interpreted as a sequence of ones and zeros, from which the data stored on the disc is restored (using a digital-to-analog converter, the digital data of an audio CD is converted into audio signals). Since only the laser beam directly "touches" the surface of the carrier, there is no wear on the carrier.

Everything would be relatively simple if the surfaces of CD-ROMs were completely flat and could rotate without horizontal deviation. In fact, as part of the drive, complex electronic circuits were required to ensure that the laser beam was focused on the surface of the disk and directed exactly to the read track.

Several methods have been developed to provide radial track tracking, but the three-beam method is the most common. The laser beam is not just directed at the surface of the disk, but is emitted by a semiconductor device and passes through a diffraction grating, which forms two additional light sources on each side of the main beam. When passed through a collimator lens, the three beams become parallel and then they pass through a prism called polarizing beam splitter(polarized beam splitter). The splitter allows the incoming beams to pass, and the returning reflected beams are rotated 90 degrees onto a photodiode that interprets the signal.

The intensities of the two side beams are measured, which should be the same as long as the beams remain on each side of the track. Any lateral movement of the disk leads to imbalance and the servo motor corrects the lens. Vertical offset is taken into account by dividing the receiving photodiode into four quadrants and placing them midway between the horizontal and vertical focal points of the beam. Any deflection of the disk causes the spot to become elliptical, causing an imbalance in the currents between opposite pairs of quadrants. In this case, the lens moves up or down, providing a circular spot shape.

CD technology provides built-in error correction systems that can correct most of the errors caused by physical particles on the surface of the disc. Every CD-ROM drive and every audio CD player uses cross-interleaved Reed-Solomon code(Cross Interleaved Reed Solomon Code - CIRC), and the CD-ROM standard provides a second level of correction using the Layered Error Correction Code algorithm. In the CIRC code, the encoder adds 2D parity information for error correction, and also interleaves the data on the disc to protect against burst errors. It is possible to correct error bursts up to 3500 bits (length 2.4 mm) and to compensate for error bursts up to 12,000 bits (length 8.5 mm) caused by small scratches.

digital audio

On records and cassettes sound signal written as analog signal. Therefore, we hear all the imperfections of the recording as interference (hiss and whistle) or other defects. To eliminate these defects in CDs, digital methods of storing "counts" (samples) as numbers are used. The process of converting an analog signal to digital is called discretization(sampling), or digitization(digitizing). The analog signal is polled many times per second and at each poll the amplitude is measured and rounded off to the nearest representable value. Obviously the higher sampling frequency(sampling rate) and the more precisely the values assigned to the amplitudes ( dynamic range- (dynamic range), the better the representation of the original.

For CD, a sampling rate of 44.1 kHz and a 16-bit dynamic range are used. This means getting 44,100 samples per second and the amplitude of the signal at the time of each sample is described by a 16-bit number, which gives 65,536 possible values. This sampling rate provides sufficient frequency response for sounds with a height of 20 kHz. However, some "audiophiles" (audiophiles) believe that this is not enough to convey the psychoacoustic effects that occur outside of human hearing. Sound is recorded on two tracks to achieve a stereo effect.

Simple calculations show (44,100 samples per second * 2 bytes * 2 channels) that one second of sound is described by 176,400 bytes with a corresponding data rate of 176.4 KB/s. A single-speed CD-ROM drive transfers data at this rate, but part of the data stream contains error correction information, which reduces the effective data rate to 150 KB/s. A CD can store 74 minutes of encoded stereo audio data, which, with error detection and correction overhead, results in a standard CD capacity of 680 MB. The table shows all the considered parameters.

Rotational speed

Constant line speed

The first generation of single speed CD-ROM drives was based on the design of audio CD players. Technology was used to rotate the disc constant linear speed(Constant Linear Velocity - CLV), i.e. the disk rotated in the same way as an audio CD, which provided a data transfer rate of 150 KB / s. The data track must pass under the read head at the same speed on the inner and outer parts of the disc. To do this, you have to change the speed of rotation of the disk depending on the position of the head. The closer to the center of the disk, the faster the disk must spin to ensure a constant stream of data. Disc rotation speed in audio CD players ranges from 210 to 540 rpm.

Because there are more sectors at the outer edge of the disc than at the center, CLV technology uses a servo motor to slow down the disc's rotational speed as it transitions to the outer tracks to maintain a constant data transfer rate from the laser read head. The drive's internal buffer memory controls the rotation speed by using a crystal oscillator to clock the buffer output data at a certain speed and keep the buffer 50% full when data is read into it. If the data is read too fast, the 50% fill threshold is exceeded and a command to slow down the spindle motor speed is sent.

If audio CDs need to be read at a constant speed, then such a requirement for CD-ROMs is not at all necessary. Essentially, the faster the data is read, the better. As CD-ROM technology has improved, the speed has steadily increased, and in 1998, drives appeared with a 32x data transfer rate of 4.8 MB / s.

For example, a 4-speed drive using CLV technology should spin the disc at about 2120 rpm when reading inner tracks and 800 rpm when reading outer tracks. Variable speed is also needed when reading audio data, which is always read at a constant speed (150 KB/s) regardless of the computer data rate. The most important factors in variable speed drives are the quality of the spindle motor that spins the drive and the software that controls the operation of the drive, as well as the positioning system, which must quickly and accurately move the read head to the desired position to access data. A simple boost rotation speed is not enough.

Another factor is the level of time utilization of the CPU: as the rotational speed, and therefore the data transfer rate, increases, so does the time that the processor must spend processing data from the CD-ROM drive. If other tasks require processor time at the same time, the CD-ROM drive will have less processing capacity and the data transfer rate will decrease. A properly designed CD-ROM drive should minimize processor usage time at a given rotational speed and data transfer rate. It is clear that the internal performance of a fast drive must be greater than that of a slow one.

For CD-ROM drives, the data buffer capacity is always given. Of course, a 1 MB buffer is definitely better than a 128 KB buffer in terms of data transfer speed. However, without a good drive management program, the marginal increase in performance hardly justifies the expense of additional buffer memory.

Constant angular velocity

CLV technology remained the dominant technology in CD-ROM drives until Pioneer, who released the first four-speed drive, released the ten-speed DR-U10X drive in 1996. This drive operated not only in the mode with the usual constant linear speed, but also in the mode with constant angular velocity(Constant Angular Velocity - CAV). In this mode, the drive transfers data at a variable speed, and the spindle motor rotates at a constant speed, like a hard drive.

Overall performance is strongly affected by access time(access time). As the speed of a CLV drive increases, access times often deteriorate because it is more difficult to accommodate the sudden changes in spindle motor speed required to maintain a constant and high data transfer rate due to the inertia of the drive itself. The CAV drive maintains a constant rotational speed, which increases the data transfer rate and reduces the seek time when the head moves to the outer edge. If in the first CLV drives the access time was 500 ms, then in modern CAV drives it has decreased to 100 ms.

Pioneer's revolutionary drive design allowed operation in CLV and CAV modes, as well as in mixed mode. In mixed mode, CAV mode was used for reading near the center of the disk, and when the head approached the outer edge, the drive switched to CLV mode. Pioneer's drive marked the end of the era of CLV-only drives and the transition to the so-called Partial CAV drives as the main form of Cd-ROM drives.

This situation continued until the development of a new generation digital signal processors(Digital Signal Processor - DSP), which could provide 16 times the data transfer rate, and in the fall of 1997, Hitachi released the first CD-ROM drive using only CAV (Full CAV) technology. It overcomes many of the problems of Partial CAV drives, in particular the need to control head position and change rotation speed to maintain a constant data rate and maintain approximately constant access times. With the new drive, it was not necessary to wait for the spindle motor speed to settle down between transitions.

Most 24-speed Full CAV CD-ROM drives in late 1997 used a constant 5000 rpm disc speed with a data transfer rate of 1.8 MB/s at the center and ramping up to 3.6 MB/s at the outer edge. By the summer of 1999, 48 times the external track data transfer rate of 7.2 MB/s was achieved at a disk rotation speed of 12,000 rpm, which corresponded to the rotation speed of many high-speed hard drives.

However, when the drive was spinning at such a high speed, there were problems with excessive noise and vibration, often in the form of a whistling sound caused by air being blown out of the drive case. Because the CD-ROM is clamped in the center, the vibration is strongest at the outer edge of the disc, ie. where the data transfer rate is maximum. Since only a small number of CD-ROMs store data on the outer edge, most high-speed drives rarely achieve the theoretical maximum data transfer rate in practice.

Applications

The question soon arose as to which applications took advantage of the speed of CD-ROM drives. Most multimedia discs have been optimized for 2-speed and at best 4-speed drives. If the video is recorded so that it can be played back in real time at a bit rate of 300 KB/s, then you do not need to exceed twice the speed. Sometimes a faster drive could quickly read information into the buffer cache, from where it was then played back, freeing the drive for other work, but this technique was rarely used.

Reading huge images from PhotoCDs proves to be an ideal use for a fast CD-ROM drive, but the need to decompress images when reading from a disc requires only 4x the data transfer rate. In fact, the only application that really needs a high data transfer rate is copying serial data to a hard drive, ie, in other words, installing software applications.

Fast CD-ROM drives are only really fast in serial data transfer, not random access. The ideal application for high continuous bit rates is high quality digital video recorded at a correspondingly high bit rate. MPEG-2 video implemented in digital versatile discs(Digital Versatile Disc - DVD) requires a bit rate of approximately 580 KB/s, while the MPEG-1 standard in the VideoCD White Paper requires only 170 KB/s. Thus, a standard 660 MB CD-ROM will be read in just 20 minutes, so high-quality video will only be of practical interest on significantly higher capacity DVDs.

Interfaces

There are three main connections on the back of CD-ROM drives: power, audio output to the sound card, and a data interface.

Most CD-ROM drives now use an IDE data interface, which can theoretically be connected to the IDE controller found in almost every PC. The original IDE hard drive was designed for the AT bus and the old IDE interface allowed two hard drives to be connected - a master and a slave. Subsequently, the ATAPI specification allowed one of them to become an IDE CD-ROM drive. The EIDE interface took it one step further by adding a second IDE channel for two more devices, which could be hard drives, CD-ROM drives, and tape drives.

Work with one of these devices must be completed before accessing any other device. Connecting a CD-ROM drive to the same channel as the hard drive will degrade the performance of the PC, as a slower CD-ROM drive will block access to the hard drive. On a PC with two IDE hard drives, the CD-ROM drive should be isolated by connecting it to the secondary IDE channel, and the hard drives should be connected as master and slave to the primary channel. The hard drives will compete with each other, but without the slow CD-ROM drive. The disadvantage of the EIDE interface is that the number of connected devices is limited to four, and all devices must be mounted internally, so expansion may be limited by the size of the PC case.

The SCSI-2 standard allows up to 12 devices to be connected to a single host adapter, which can be internal or external. SCSI allows all devices on the bus to be active at the same time, although only one device can transmit data. The physical localization of data in devices is relatively time consuming, so while one device is using the bus, any other device can position heads for read and write operations. The latest Fast Wide SCSI specification supports a maximum transfer rate of 20MB/s compared to EIDE's 13MB/s, and with built-in intelligence, SCSI devices require less CPU attention than IDE devices.

The advantages of the SCSI interface compared to the IDE are also manifested when using PC resources, in particular the IRQ interrupt request lines. Due to the large number of additional cards and devices, modern PCs place increased demands on the use of IRQ, leaving little room for further expansion. The primary EIDE interface is usually allocated IRQ 14 and the secondary IRQ 15, so four devices are added at the expense of two interrupt lines. The SCSI interface is less resource intensive because, regardless of the number of devices on the bus, only one IRQ line is required for the host adapter.

In general, the SCSI interface provides more expansion potential for the PC and provides better performance, but it is significantly more expensive than the IDE interface. The current preference for internal EIDE drives turns out to be more convenient and cheaper than technical excellence, so the SCSI interface is chosen only for external CD-ROM drives.

Comparison of DMA and PIO mode

Traditionally, CD-ROM drives used to transfer data. programmable I/O(Programmable Input/Output - PIO), not direct memory access(Direct Memory Access - DMA). This was justified in early designs because the hardware implementation was simpler and suited to low data rate devices. The disadvantage of this method is that the processor controls the data transfer. As the data transfer rate of CD-ROM drives increased, so did the processor load, so 24- and 32-speed drives completely occupied the processor in PIO mode. Processor load depends on several factors, such as the PIO mode being used, the IDE/PCI bridge design in the computer, the capacity and buffer design of the CD-ROM drive, and the CD-ROM drive device driver.

Transferring data using DMA is always more efficient and takes only a few percent of the CPU time. Here, a special controller manages the transfer of data directly to system memory, and the processor is only required to initial memory allocation and minimal acknowledgment(handshaking). Performance is device dependent, not system dependent. DMA devices should provide the same performance regardless of the system they are connected to. DMA has long been a standard feature on most SCSI systems, but only recently has it become widely used for interfaces and IDE devices.

TrueX Technology

In order to allow users to run applications directly from a CD without transferring to a hard drive, Zen Research has taken an original approach to improving the performance of CD-ROM drives when developing TrueX technology - to improve data transfer speed and access time, and not just spin the disk faster. A conventional CD-ROM uses a single focused laser beam to read a digital signal encoded in tracks of tiny pits on the surface of the disc. The Zen Research method uses ASIC(Application-Specific Integrated Circuit - ASIC) for illuminating multiple tracks, simultaneously detecting them, and reading from the tracks in parallel. ASICs include analog interface elements such as Digital Phase-Locked Loop (DPLL), digital signal processor, servo motor controller, parallel-to-serial converter, and ATAPI interface. Optionally, you can connect an external SCSI or IEEE 1394 interface circuit.

A split laser beam, used in conjunction with a multi-beam detector array, illuminates and detects multiple tracks. An ordinary laser beam is passed through a diffraction grating, which splits it into seven discrete beams (such drives are called multipath- multibeam), illuminating seven tracks. Seven beams are fed through the mirror to the lens and then to the disk surface. Focusing and tracking are provided by the central beam. Three beams on each side of the center are read by the detector array when the center beam is on the track and focused. The reflected beams return along the same path and are directed by the mirror to the detector array. The multi-beam detector has seven detectors aligned with reflective tracks. Conventional detectors are provided for focusing and tracking.

Although the mechanical elements of the CD-ROM drive have been slightly changed (disk rotation and read head movement remain the same), the disc media format follows the CD or DVD standard, and the usual approach is used for searching and tracking. TrueX technology can be used in CLV and CAV drives, but Zen Research focuses on CLV to ensure consistent data transfer rates for the entire drive. In any case, a higher transfer rate is achieved with a slower rotation of the disk, which reduces vibration and improves reliability.

Kenwood Technologies released the first 40-speed TrueX CD-ROM drive in August 1998, and six months later developed a 52-speed drive. Depending on the operating environment and media quality, the Kenwood 52X TrueX CD-ROM drive delivers data transfer rates of 6.75 - 7.8 MB/s (45x - 52x) across the entire disc. For comparison, let's point out that a typical 48-speed CD-ROM drive provides 19x speed on internal tracks and reaches 48x speed only on external tracks. At the same time, its rotation speed is more than twice as high as compared to the Kenwood Technologies drive.

CD-ROM standards

To understand the CDs themselves and which drives can read them, you first need to get acquainted with the disc formats. Typically, CD standards are issued as books with colored covers, and the standard itself is named after the color of the cover. All CD-ROM drives are Yellow Book and Red Book compliant and have built-in digital-to-analog converters(Digital-to-Analog Converter - DAC), which allows you to listen to Red Book audio discs through headphones or audio output.

Red Book

The Red Book is the most common CD standard and describes the physical properties of a CD and the encoding of digital audio. It defines:

Audio specification for 16-bit Pulse Code Modulation (PCM).
Specification of the disk, including its physical parameters.
Optical styles and parameters.
Deviations and frequency of block errors.
Modulation and error correction system.
Control and display system.

Each piece of music recorded on a CD meets the Red Book standard. It basically allows sounding for 74 minutes and splitting information into tracks(tracks - tracks). A later addendum to the Red Book describes the CD Graphics option using subcode channels R through W. The addendum describes various uses of subcode channels, including graphics and MIDI.

Yellow Book The Yellow Book was released in 1984 to describe the CD extension for storing computer data, i.e. CD-ROM (Compact-Disc Read-Only Memory). This specification contains the following:

Disc specification, which is a copy of a part of the Red Book.
Modulation and error correction system (from the Red Book).
Optical styles and parameters (from the Red Book).
Control and display system (from the Red Book).
A digital data structure that describes the sector structure, ECC and EDC for a CD-ROM disc.

CD-ROM XA

As a separate extension of the Yellow Book, the CD-ROM XA specification contains the following:

Disc format including Q channel and sector structure when using Mode 2 sectors.
Data retrieval structure based on the ISO 9660 format, including file interleaving, which is not available in Data Mode 2.
Audio coding using levels B and C of ADPCM modulation.
Video coding, i.e. still images.

Currently, only CD-ROM XA formats such as the CD-I Bridge formats for Photo CD VideoCD plus of Sony's Playstation system are used.

Green Book

The Green Book describes the CD-Interactive (CD-I) disc, player and operating system and contains the following:

CD-I disc format (track and sector structure).
Data retrieval structure based on the ISO 9660 format.
Audio data using levels A, B and C of ADPCM modulation.
Real-time still video encoding, decoder and visual effects.
Compact Disc Real Time Operating System (CD-RTOS).
Basic (minimum) system specification.
Movie extension (MPEG cartridge and software).

A CD-I disc can store 19 hours of audio, 7,500 still pictures, and 72 minutes of full screen full motion video (MPEG) in standard CD format. CD-I discs are obsolete now.

Orange Book

The Orange Book defines CD-Recordable discs with multisession capability. Part I defines CD-MO (Magneto Optical) magneto-optical rewritable discs; part II defines CD-WO (Write Once) discs; Part III defines rewritable CD-RW (Rewritable) discs. All three parts contain the following sections:

Disc specification for unrecorded and recorded discs.
Pre-groove modulation.
Data organization, including linking.
Multi-session and hybrid discs.
Tips for reflectivity measurement, power control, and more.

White Book

Disc format, including track usage, VideoCD information area, segment playback area, audio/video tracks, and CD-DA tracks.
A data lookup structure conforming to the ISO 9660 format.
MPEG audio/video track encoding.
Playback segment element encoding for video sequences, stills, and CD-DA tracks.
Playback sequence descriptors for programmed sequences.
User data fields for data scanning (fast forward and backward scanning is allowed).
Examples of playback sequences and playback controls.

Up to 70 minutes of full motion video is encoded in the MPEG-1 standard with data compression. The White Paper is also called Digital Video (DV). A VideoCD disc contains one data track recorded in CD-ROM XA Mode 2 Form 2. It is always the first track on the disc (Track 1). This track contains the ISO 9660 file structure and CD-I application, as well as the VideoCD Information Area, which contains general information about the VideoCD disc. After the data track, video is recorded on one or more subsequent tracks during the same session. These tracks are also recorded in Mode 2 Form 2. The session ends when all tracks have been recorded.

Blue Book

The Blue Book defines the Enhanced Music CD specification for multi-session compressed discs (ie non-recordable discs) containing sound and data sessions. The discs can be played with any audio CD player and on a PC. The Blue Book contains the following:

Disc specification and data format, including two sessions (audio and data).
Directory structure (ISO 9660), including directories for CD Extra information, images and data. The CD Plus information file format, image file formats, and other codes and file formats are also defined.
MPEG still image data format.

CDs conforming to the Blue Book specification are also called CD-Extra or CD-Plus. They contain a mixture of data and audio recorded in separate sessions to prevent playback of data tracks and possible damage to high-quality home stereo systems.

CD-I Bridge

CD-I Bridge is a Philips and Sony specification for discs designed to be played on CD-I players and PCs. It contains the following:

A disc format that identifies CD-I Bridge discs as conforming to the CD-ROM XA specification.
Data retrieval structure in accordance with ISO 9660. The application program CD-I is required and is stored in the CDI directory.
Audio data encoding, which includes ADPCM and MPEG.
Video encoding for CD-I and CD-ROM XA compatibility.
Multi-session disk structure, including sector addressing and volume space.
Data for CD-I since all CD-I players must read CD-I Bridge data.

Photo CD

The Photo CD specification is defined by Kodak and Philips based on the CD-I Bridge specification. It contains the following:

General disc format, including program area layout, index table, volume descriptor, data area, Q-channel subcode skew, CD-DA clips, and microcontroller-readable sectors.
Data search structures, including the directory structure, the INFO.PCD file, and the microcontroller-readable sector system.
Image data encoding, including description of image encoding and image packages.
ADPCM files for simultaneous playback of sound and images.

A lot of information on CD-ROM drives is contained on the site http://www.cd-info.com/.