What is CD-ROM. CD-ROM drives CD-ROM drive

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 some 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 store the contents of an optical disc without having to copy it to your hard drive.

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. Please 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 CD-RW discs to be as reliable as possible, one technique is needed to prevent buffer overruns. 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 a USB keyboard outside of the Windows GUI, then your 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 is 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, speakers, joysticks, tape and floppy drives, scanners, camcorders, MP3 players, and many others. However, when connecting multiple devices to the same low-speed USB 1.1 port, there may be some issues that should be resolved by switching 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 ...

CD-ROM drive device.

CD-ROM drive is a complex electronic-optical-mechanical device for reading information from laser discs. A typical drive consists of an electronics board (sometimes two or even three boards - a spindle control circuit and an opto-receiver amplifier separately), a spindle assembly, an optical read head with a drive for its movement, and disk loading mechanics.

On the electronics board are placed:

  • circuit for amplifying and correcting the signal from the optical head;
  • signal PLL circuit and ACS spindle;
  • Reed-Solomon code processing processor;
  • ACS circuits for beam focusing and dynamic track tracking;
  • optical head movement control circuit;
  • control processor (logic);
  • buffer memory;
  • interface with controller (IDE/SCSI/other);
  • connectors for interface and audio signal output;
  • block of mode switches (jumpers/jumpers).

A typical drive consists of an electronics board, a spindle motor, an optical readhead system, and a disc loading system. The electronics board contains all the control circuits of the drive, the interface with the computer controller, the interface connectors and the sound signal output. Most drives use a single electronics board, however, in some models, separate circuits are placed on auxiliary small boards.

Spindle assembly (motor and actual spindle with disc holder) is used to rotate the disc. Typically, the disk rotates at a constant linear speed, which means that the spindle changes speed depending on the radius of the track, from which the optical head is currently reading information. When moving the head from the outer radius of the disk to the inner radius, the disk must quickly increase the speed of rotation by about half, so a good dynamic response is required from the spindle motor. The motor is used for both acceleration and deceleration of the disc.

On the axis of the spindle motor (or in its own bearings) the spindle itself is fixed, to which the disk is pressed after loading. The surface of the spindle is sometimes covered with rubber or soft plastic to eliminate disc slippage, although more advanced designs rubberize only the top clamp to increase the accuracy of placing the disc on the spindle. Pressing the disk to the spindle is carried out using the upper clamp located on the other side of the disk. In some designs, the spindle and clamp contain permanent magnets whose attractive force presses the clamp through the disk against the spindle. Other designs use helical or flat springs for this.

Optical head system consists of the head itself and its movement system. The head contains a laser emitter based on an infrared laser LED, a focusing system, a photodetector and a preamplifier. Focus system represents a movable lens driven by an electromagnetic voice coil system (voice coil), made by analogy with a movable loudspeaker system. Changes in the strength of the magnetic field cause the lens to move and refocus the laser beam. Due to the low inertia, such a system effectively monitors the vertical beats of the disk even at significant rotation speeds.

Head movement system has its own drive motor that drives the carriage with an optical head using a gear or worm gear. To eliminate backlash, a connection with an initial voltage is used: with a worm gear - spring-loaded balls, with a toothed gear - pairs of gears spring-loaded in different directions. A stepper motor is usually used as a motor, and much less often a DC collector motor.

Disc loading system There are three options: using a special cassette for a disk (caddy) inserted into the receiving niche of the drive (similar to how a 3 "floppy disk is inserted into a drive), using a drawer (tray), on which the disk itself is placed, and using a retractable Tray systems usually contain a special motor that provides the tray extension, although there are designs (for example, Sony CDU31) without a special drive, pushed in by hand.Systems with a retractable mechanism are usually used in compact CD-Changers for 4-5 discs, and necessarily contain a motor for retracting and ejecting discs through a narrow charging slot.

On the front The drive usually has an Eject button for loading/unloading a disc, a drive access indicator, and a headphone jack with electronic or mechanical volume control. Some models have added a Play/Next button to start playing audio discs and switch between audio tracks.

Most drives also have a small hole on the front panel, designed for emergency ejection of a disk in cases where it is impossible to do it in the usual way - for example, if the tray drive or the entire CD-ROM fails, if the power goes out, etc. You usually need to insert a pin or a straightened paperclip into the hole and gently press - this unlocks the tray or disc case, and you can pull it out manually (although there are drives, such as Hitachi, in which you need to insert a small screwdriver into such a hole and rotate it located behind the front drive panel axis with slot).


Structural diagram of a CD-ROM


Functional diagram of a CD-ROM

A very important component of the device is an optical-electronic system for reading information. Despite its small size, this system is a very complex and precise optical device.

It consists of:

  • servo control systems for disk rotation;
  • servo systems for positioning the laser reader;
  • autofocus servo systems; radial tracking servo system;
  • reading systems;
  • laser diode control circuits.

The disk rotation servo control system ensures the constancy of the linear speed of the reading track on the disk relative to the laser spot. In this case, the angular velocity of disk rotation depends both on the distance of the read head to the center of the disk and on the conditions for reading information.


The servo system for positioning the head of information reading ensures a smooth lead of the head to a given recording track with an error not exceeding half the width of the track in the modes of searching for the required piece of information and normal playback. The movement of the reading head, and with it the laser beam, across the disk field is carried out by the head motor. The operation of the motor is controlled by forward and reverse motion signals from the control processor, as well as signals generated by the radial error processor.

The radial tracking servo system ensures that the laser beam is kept on the track and optimal conditions for reading information. The operation of the system is based on the method of three light spots. The essence of the method is to divide the main laser beam using a diffraction grating into three separate beams with a slight difference. The central light spot is used to read information and to operate the autofocus system. Two side beams are located in front and behind the main beam with a slight offset to the right and left. The misalignment signal of these beams from the positioning sensors affects the tracking drive, causing, if necessary, correction of the position of the central beam.

The operability of the radial tracking system can be monitored by changing the error signal supplied to the tracking drive.

Control and management of the vertical movement of the focusing lens is carried out under the influence of servo focus. This system ensures accurate focusing of the laser beam during operation on the working surface of the disc. After the CD is loaded and started, focus adjustment begins according to the maximum level of the output signal of the photodetector matrix and the minimum level of the error signal of the fine focus detectors and the passage of focus zero. At the start of the disk, the CD-ROM control processor generates correction signals that provide multiple (two or three) movement of the focal lens necessary for accurate focusing of the beam on the disk track. When the focus is found, a signal is generated that allows the reading of information. If after two or three attempts this signal does not appear, the control processor turns off all systems and the disk stops. Thus, the operability of the focusing system can be judged both by the characteristic movements of the focal lens at the moment the disk starts, and by the signal for starting the disk acceleration mode when the laser beam is in focus.

The information reading system contains a photodetector matrix and differential signal amplifiers. The normal operation of this system can be judged by the presence of high-frequency signals at its output when the disk rotates.

The laser diode control system provides the nominal excitation current of the diode in the modes of starting the disk and reading information. A sign of normal operation of the system is the presence of an RF signal with an amplitude of about 1 V at the output of the reading system.

Systems for writing, reading and post-processing information determine the overall functional diagram of the CD-ROM, presented in the functional diagram. In addition to the systems discussed above, it includes a clock generator that provides clock signals to all nodes of the CD-ROM, and an EFM demodulator that converts 14-bit code packets from the disk into an 8-bit serial code. Further, the information enters the digital data processor, which, together with the system control processor, is the heart of the entire device. This is where data deinterleaving and error correction takes place. The task of data interleaving when recording information is to "stretch" each byte of information into several recording frames. In this case, if even a few frames of information are lost as a result of mechanical damage to the disk surface, the result of data deinterleaving will be the presence of small errors in individual bytes. Such errors are corrected by an error correction circuit.

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. Such disks are most often used to store important information that 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 of 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 and DVD+R discs can be 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.

Long gone are the days when the archive of programs and documents of an ordinary user of a personal computer could fit in several boxes of floppy disks. Document sizes with graphic illustrations can be overwhelming. Distributions of modern software already occupy hundreds of megabytes, and in most cases are delivered on CD-ROMs.

The computer industry has created many devices that allow you to store large amounts of information. Leaving aside tape drives intended for archival storage only, let's call magneto-optical drives, ZIP and Jazz drives, removable magnetic disks, PD-CD devices, advanced DVD devices, and so on. If you're tired of dusting boxes full of floppy disks and your hard drive is full, then it's time to consider purchasing a new external storage device.

But what to choose?

Each of these devices has its own advantages and disadvantages. Therefore, before you decide on anything, you should think about how and for what you will use this device, as well as estimate how much money you are willing to spend on its acquisition.

Until recently, you could hardly like the idea of ​​buying a CD-R burner to create a personal data archive. Just a year ago, it cost more than a thousand dollars, and the procedure for writing files to CD-R discs required special training and difficult-to-use software. Before burning a CD-R disc, it was necessary to pre-assemble all the files on the hard drive, as well as create a CD image file hundreds of megabytes in size. In addition to the CD-R burner, you also needed to purchase a high-capacity, fast hard drive and a SCSI controller. In addition, there was no way to add new files to the CD-R or replace old ones. If you made a mistake while preparing the files or when burning, the CD-R turned out to be irrevocably damaged.

Everything has changed today. The cost of CD-R recorders has plummeted to around $400-$500. At the same time, you can buy a blank CD-R, which can hold up to 650 megabytes of data, for $7-8, which is already quite inexpensive. A new recording principle has been developed (the so-called packet recording), as a result of which working with a CD-R disc has become not much more difficult than with a regular floppy disk.

Recordable CD technology hasn't stood still either. This year saw the introduction of the CD-RW, which, unlike the CDR disc, can be rewritten up to 1,000 times. This disc only costs $20, so it's ideal for backing up information, creating high-capacity archives, or mocking up CD-R discs before burning. By the way, the CD-RW Reader/Writer/Rewriter costs only $100 more than a similar CD-R Burner.

As a result, the CD-R and especially CD-RW recorder has become much more attractive to users. Here is a list of just some of the applications for such devices:

  • prototyping of CD-ROM discs before batch production at the factory;
  • backing up CD-ROMs with software distributions, as well as music discs;
  • archiving large data sets, such as multimedia files;
  • moving data over a long distance (for example, to another city), when the amount of data does not allow it to be transmitted over the Internet or through other electronic channels;
  • creation of personal libraries of software or documentation;
  • storage of a large number of graphic images in the form of electronic albums.

Three CD burning technologies

To date, two technologies for the manufacture and recording of CDs are best known, which are very different from each other. The third, which we will also cover in our article, is just beginning to gain popularity.

Pressing aluminum rims

The first and oldest technology involves the use of extremely expensive factory equipment. It allows you to create so-called aluminum wheels. These disks are made by pressing using a prefabricated matrix. The working surface of the disk is made of aluminum. Aluminum disks are also called CD-ROM disks (from the words Read Only Memory - only readable memory), since they only allow reading information, but not writing it.

You are probably familiar with aluminum wheels. This technology is used to make music CDs and distribution disks with software, games, databases, and multimedia directories. One such disc can contain up to 650 MB of data or up to 74 minutes of music.

The minimum number of disks manufactured at the factory is usually 500-1000 pieces. It is unprofitable to produce small batches, since the cost of manufacturing a disk matrix is ​​too high. However, the production cost per CD-ROM in a large batch is about $1.50, which is very cheap.

CD-ROMs are durable enough that if you don't scratch the disc's surface, they will last for decades. Don't be embarrassed that CD-ROMs purchased from the pirate market are not always readable. In the pursuit of profit, they are often manufactured in violation of technology. We have not heard of problems with reading licensed discs.

One time write to gold disc

The second technology allows information to be written to a CD once, for which relatively inexpensive devices can be used. Recording is performed on blank gold-colored discs, which are commonly called gold (although the working surface of a Verbatim DataLife CD-R disc is blue). Another name is CDR (CD Recordable) discs. During the recording process, a thin layer of gold is burned along the working track with a powerful laser. A CD-R disc can be read on a conventional CD-ROM reader. If you have burned a CD-R music disc, you can play it in a regular CD player.

Unlike aluminum CDs, gold CDs are more suitable for piece production. A blank CD-R disc costs about $7-10 and a burner costs $400 to $1,000, so you can set up a mini-production of these discs at home or at work.

If you are concerned about the reliability of CD-R discs as a storage medium, then usually manufacturers guarantee the safety of data for 30 years. This is quite enough. After 30 years, you will be able to write the contents of your entire CD-R box onto some new type of media, just as you can now write the contents of all your floppy disks to a single CD-R disc.

However, there is one problem with CD-R discs. Some CD-ROM readers do not always read CD-R discs well. This is due to the fact that the track burned by the laser does not look the same as the one embossed on the aluminum disc. However, in most cases this problem does not occur.

Multiple overwriting by changing the phase state

In addition to the two technologies listed above, a third one, which allows multiple rewriting of CDs, has recently begun to spread actively. This technology is based on changing (again with the help of a laser) the phase state of a substance on the working surface of a CD. If this substance is in an amorphous state, it has a low reflectivity, and if in a crystalline state, it has a high one. Externally rewritable CDs are similar to aluminum CDs and are called CD-RWs (CD Rewritable).

The technology of recording with a change in the phase state of matter did not appear today. It has long been used in PD-CD drives. Note, however, that PD-CDs use a non-standard data format, so they can only be used in PD-CD devices. Magneto-optical discs have a similar problem. As for CD-RW discs, they are standardized and even compatible with DVD readers, which may appear this year.

CD-RWs cost around $20, which is not much more expensive than CD-Rs and noticeably cheaper than magneto-optical drives. If you need a means to store a lot of changing data, then CD-RW discs can help you save a lot of money.

Unfortunately, you will not be able to read CD-RW discs in conventional CD-ROM readers. Only the latest MultiRead devices and DVD drives are capable of reading CD-RW discs. Note, however, that this disadvantage is also inherent in magneto-optical discs and PD-CD discs.

The ability to burn CD-RW discs will cost you an additional hundred dollars, which is not outrageous for the average user. We recently purchased one such device, such as the MP6200S. It's made by RICOH and costs just $700 with a SCSI controller, interface cable, and two blank CDs. This product is, as it were, a combination of two devices - for recording CD-R discs, as well as for reading and writing CD-RW discs.

What about the speed of the MP6200S?

When writing, it is not too high - the same as double-speed CD-ROM readers. However, CD-RW discs, like CD-ROMs and CD-R discs, are read by the MP6200S at six times the speed. Therefore, if you use CD-RW discs not as working discs, but only for archiving and backing up data, this speed will be quite sufficient.

Data formats recorded on CDs

The foundation for the technology of writing data to compact discs was laid back in the 1980s. Without delving deep into history, we note that since then several standards for the storage format of data on compact discs have been developed and implemented, and today you can come across any of them. Confusion with data formats usually leads to problems when writing your own CD-R, so you should understand this issue.

So, let's deal with data formats.

  • CD-DA

The CD-DA (CD Digital Audio) format was developed in 1982 and, as the name implies, is intended for audio CDs. In accordance with this format, up to 99 tracks can exist on a disc, arranged sequentially one after another (Fig. 1). Gap lengths of 2 seconds are inserted between tracks.

Rice. 1. Tracks on a CD-DA disc

At the beginning of the track, a session header is written, which is called the lead-in. The size of the lead-in area is 120 seconds. The track ends with a lead-out area containing all zeros. This area is for the CD player to detect the end of a track.

In the CD-DA format, data is written to tracks in blocks of 2352 bytes in size, and there are no means of error control when reading data.

The CD-R burner allows you to create CD-DA audio discs for music lovers to enjoy.

  • CD-ROM

There is only one track on a CD-ROM disc, divided into fixed size data blocks (Figure 2).

Rice. 2. CD-ROM track

The CD-ROM format is designed to store computer data and programs, so special error control tools were provided in it. As a result, due to the addition of service areas in the data block, out of 2352 bytes, only 2048 bytes of space remained.

The first data CDs were created in the CD-ROM format. Most aluminum software and operating system distribution CDs are also made in this format.

Note that the CD-ROM format assumes the use of two types of sectors. The first type (Mode1) is intended for storing computer data, and the second (Mode 2) is for storing compressed graphic, sound or video data. The sector of the first type stores 2048 bytes of data and an error correction code. In vectors of the second type, error correction is not provided, so 2336 bytes are allocated for data.

  • mixed format

In mixed-format CDs, tracks of the CDDA type and CD-ROM type are recorded on the same disc with Mode 1 sectors. This allows you to store computer and audio data together (Fig. 3).

Rice. 3. Mixed disc tracks

The mixed format opens up new opportunities for programmers, as it allows you to add high-quality sound to programs. There is, however, a problem - a CD-ROM reader cannot read computer data while playing audio tracks. The way out is simple - before starting, you need to rewrite the program from the CD to the hard disk or to the RAM.

Another problem is that mixed-format CDs have a CD-ROM track written first, followed by one or more CDDA tracks. If you insert such a disc into a conventional audio CD player, the latter may attempt to play the data as sound. This can shock the listener and damage the audio equipment, especially if the audio amplifier is turned on at full power. This problem is successfully solved by using the Enhanced CD format, which we will talk about a little later.

  • CD-ROM/XA

After some time, the CD-ROM format was expanded, resulting in the CD-ROM / XA format (XA is an eXtended Architecture, that is, an extended architecture).

What has been expanded?

It became possible to alternate sectors of computer data, as well as graphic, audio and video data on one track, which is very convenient for multimedia programs (Fig. 4). By writing appropriately prepared data to a track, it is possible to organize multi-threaded reading when computer and multimedia data are read simultaneously.

Rice. 4. Interleaving of sectors of computer and multimedia data

Sectors of various types are used to store computer and multimedia data. Form 1 sectors (with error correction) are used for computer data, and Form 2 sectors (without correction code) are used for multimedia data.

You can create mixed-format discs by writing a CDROM/XA track with Form1 sectors first, followed by one or more CDDA audio tracks.

  • PhotoCD

When burning a CD-R disc in CD-ROM format, it is necessary to write all the tracks in one go, or, as they say, in one session. Once you have burned data to a CD, you cannot add new data to it even if there is free space left on the CD-R. Philips and Codak have developed the PhotoCD format to address this shortcoming. If a CD-R is written in PhotoCD format, you can add new data to the data recorded during the first session by performing one or more additional recording sessions. At the physical level, the PhotoCD format is implemented using the CD-ROM/XA format. PhotoCDs are typically used to store graphic images.

Older CD-ROM drives cannot read such discs, but this problem does not exist with newer devices.

  • Multisession CD-ROM/XA discs

When creating a disk for storing computer data in the CD-ROM/XA format, it is possible to record tracks not all at once, but one or several in one recording session.

On fig. 5 we have shown the structure of the disk containing the data of two sessions. During the first session, one track was recorded, and during the second session, three more.

Rice. 5. The structure of the disk containing the data of two sessions

Note that each session starts with a lead-in and ends with a lead-out, with the last lead-out being three times smaller than the previous ones. There are gaps between the tracks of the second session.

If you have created a CD-ROM/XA multi-session disc in several steps, the ion will look like a single-session disc when read. Data from different sessions is merged and made available at the same time. Again, as with the PhotoCD format, the CD-ROM drive must be compatible with the CD-ROM/XA standard to read multi-session CDs.

Most often, when creating CDs for data storage, you will have to choose between the CD-ROM and CD-ROM/XA formats. If the CD will be burned in one session and you do not plan to write additional data to it in the future, you should select the CD-ROM format. If you are going to burn a CD in several steps, you should stop at the CD-ROM / XA format.

  • Enhanced CD

As we just said, the CD-ROM/XA format allows you to combine audio and data tracks on the same disc. In this case, the data track is written first, otherwise it will not be available to programs. Here comes the problem of trying to play such a disc in a conventional audio CD player, which we have already discussed.

The Enhanced CD format solves this problem by allowing data to be written on the last track of the disc instead of the first track. The first few tracks of the disc are recorded in one session and can be used to store audio data. The track for storing computer data is recorded in the second session (Fig. 6).

Rice. 6. Enhanced CD Format

If you insert an Enhanced CD into a regular audio CD player, it will look like a normal music CD because the player can only play tracks recorded during the first session. As for the data track, it is currently available only for Windows 95 and Macintosh OS applications.

In the literature, you can find other names for this format - CD Extra or CD Plus.

The CD-I (CD Interactive) format is designed for interactive multimedia applications that run on small computers connected to a home TV.

  • CD-I Bridge

The CD-I Brige format is a set of specifications that define how CD-I information is written on CD-ROM/XA discs. These discs, unlike CD-I discs, can be read on computers. The CD-I Brige format is used for PhotoCDs and VideoCDs.

  • VideoCD

The VideoCD format has appeared relatively recently and is used, as a rule, for recording conventional video films to compact discs. Video CDs are an alternative to conventional video cassettes and, with a sufficiently powerful computer, provide good quality full-screen images.

The first track of a VideoCD is for data storage and is recorded in the CD-ROM/XA format. This track stores programs as well as information about the CD itself. The next few tracks contain video information that is compressed according to the MPEG standard.

  • CD-UDF

A new format that uses packet writing. The universal disk format CD-UDF (Universal Disk Format) allows you to organize the access to a CDR or CD-RW disk during recording and reading as a conventional disk drive or floppy disk. We will talk about this format in more detail a little later.

CD file systems

When burning a CD-R with computer data, you must select a file system type for it. The choice is made based on which operating system the disk is intended for. You can, for example, burn a CD with a file system capable of handling long Windows 95 filenames. Note, however, that files and directories with long filenames will not be available in an MS-DOS environment.

Let's look at the main types of standards for CD file systems. These standards define the logical format of the data written to the disc.

  • ISO-9660

The ISO-9660 standard is divided into three levels. The first level imposes serious restrictions on the recorded files - they cannot be fragmented, the names of files and directories must consist of 8 characters plus 3 characters of the name extension. The second level removes restrictions on the names of files and directories, but leaves a restriction on the absence of file fragmentation. In the third level, this restriction is also lifted.

In its purest form, the ISO-9660 Level 1 standard is used to write CD-R discs intended to be read in an MS-DOS environment. As for the Microsoft Windows 95 and Microsoft Windows NT operating systems, standards have been developed for them with the romantic names Romeo and Joliet.

  • Joliet

The Windows 95 operating system is famous not only for its long filenames, but also for its clever way of making those filenames compatible with MS-DOS programs. For each file with a long name in the directory, several descriptors are created, one of which contains an alternative name in MS-DOS format, and the rest contain the original name, possibly divided into several parts (because the size of the descriptor is fixed). Windows 95 applications work with the original filename, while MS-DOS programs use the alternate filename. Externally, an alternative name looks like an abbreviation of the full name, at the end of which there is a tilde character "~" and a number.

The Joliet standard allows filenames up to 64 characters long, and also allows for the alternative names described above to be created on the CD. Additionally, this standard allows names to be written in Unicode.

If your CD is for Windows 95 and Windows NT version 4.0 or higher, has long file names, and requires compatibility with MS-DOS programs, then you should use the Joliet standard. Note that earlier versions of Windows NT cannot read Joliet discs.

  • Romeo

The Romeo standard provides another option for writing files with long names to a CD. The name can be 128 characters long, but does not use Unicode encoding. Alternate names are not created in MS-DOS, so MS-DOS programs will not be able to read files from such a disk.

You can select the Romeo standard only if the drive is intended to be read by Windows 95 and Windows NT applications. If you limit filenames to 31 characters, the Romeo CD will also run on a Macintosh.

The hierarchical file system of Macintosh computers is not compatible with any other file systems and is called the Hierarchical File System (HFS). Such a file system can also be created on a CD.

Note that you can burn a so-called hybrid disk, which has several partitions with different file systems. For example, you can create a CD that can be read on both the Windows operating system and the Macintosh operating system.

Burning a CD-R disc in one session

The originally developed method for burning ISO-9660 CD-R discs requires that all tracks be written in one session. This method is called disk-at-once, that is, the entire disk is written at once.

Before you can burn an ISO-9660 CD, you must place all files in a separate directory on your hard drive. Of course, there must be enough free space on the hard disk. During the preparation of the source directory, you should check that the names of the directories and files comply with the ISO-9660 standard.

Next, run the CD-creation program that comes with the CD-R burner. The best known programs are Adaptec Easy CD Pro, Corel CD Creator, and WinOnCD, although there are several others. This program needs to tell you what files and directories you want to burn to disk. This procedure is performed by simply moving the icons of files and directories to the program window specially designed for this using the mouse (Fig. 7).

Rice. 7. Selecting directories to burn to a CD

After preparing the source files, you have two options for burning a CD-R disc.

First, you can create an ISO-9660 disk image file so that you can then burn one or more CD-R discs using this file as a source file. This method is convenient for copying CD-ROMs, but requires additional free space on a hard disk up to 650 megabytes.

Second, you can create a virtual disk image that contains only links to the files being written, but not the files themselves. Thus, when recording, free space on the computer's hard disk is saved.

Why not always use only a virtual disk image?

The fact is that the process of writing a CD-R disc must be continuous. This places serious demands on the performance of the disk system. If the internal buffer of the recorder is empty as a result of the delay in data arrival, the burning process will be interrupted and you will only have to throw away the damaged CD-R disc. When you prepare a disk image as a file, the data will flow to the burner more evenly than when using a virtual disk image.

To reduce the risk of CD-R disc corruption due to insufficient data rates or other errors, it is recommended that you perform testing before burning. In the test mode, the program simulates writing data to a CD-R disc, but the recording itself is not performed. Although the test takes a long time, it should not be neglected.

If, after testing, it turns out that the system performance is not sufficient to write from a virtual disk image file, you can try to create a physical disk image file and test again.

After testing, select the recording mode and wait. Depending on the speed of the device, the recording procedure can take from ten minutes to an hour.

When the process is complete, the burner will close the session and the disc, resulting in a table of contents area of ​​approximately 13 megabytes on the disc.

Burning a CD-R disc in multiple sessions

The data burning procedure just described assumes that you have prepared all the files for burning in advance, and then transferred them to a CD-R disc in one go, or, as they say, in one session. However, this is not always convenient, since you need to prepare all the data at once.

Modern CD-R disc burners make it possible to form a disc gradually, over several sessions. In each session, you can record one or more tracks, while the hard disk space will be used more economically.

When a session ends, the lead-in and lead-out areas are written to disk. Note that since these areas take up a lot of space, multi-session recording is usually used to add relatively large amounts of data to a CD-R disc. In addition, an ISO-9660 disc can contain no more than 99 tracks, which imposes an additional limitation on the areas of application of multi-session recording.

We draw your attention to a very important circumstance that must be taken into account when creating discs with several sessions. When you record the second and subsequent sessions, you must specify that this session should be linked to the previous one. In this case, and only in this case, the data recorded during several sessions will look like recorded in one go.

How does it work?

At the end of the first session, a table of contents is placed on the first track, which contains links to the recorded files and directories. When the second session ends, a table of contents is also created on the second track. If, when recording the second session, you indicated a link to the first track, then a link to the first track's TOC is placed in the TOC of the second track. Thus, the TOCs of the two tracks are, as it were, combined into one common TOC.

When you insert a multi-session disc into a CD-ROM drive, all of these TOCs are read and combined. As a result, the user sees the entire disc, as if it were written in one session.

Unfortunately, there are sometimes issues with multi-session discs that you should be aware of.

First, multi-session discs must be written in CD-ROM/XA format. Such discs may not be recognized as multi-session by older CD-ROM readers. In this case, only the data of the first session will be available. The device's documentation should say whether it can handle CD-ROM/XA discs.

Second, when you record your first session, you may mistakenly specify CD-ROM instead of CD-ROM/XA. In this case, even some newer CD-ROM readers may not recognize the extra sessions.

Third, you may forget to link the current session's TOC to the previous session's TOC. As a result, only the data of the last session will be available for reading data.

CD from which you can boot the operating system

There is one area of ​​​​application of conventional floppy disks where they still had no competitors - these are boot floppy disks for installing operating systems. Everyone has at least one in stock so that you can restore your computer after the crash of the operating system or hard drive. However, bootable CDs have now appeared, which can take even this bread from floppy disks.

The ability to boot an operating system from a CD has long been a feature of Compaq's Proliant series servers. When you purchase this server, you get a Smart Start Operatng Systems CD set with it. Using this set, you can install one of several operating systems directly from the CD. disks.

Many modern computers allow you to boot the operating system from a CD. This feature can be enabled using the BIOS Setup program. Note that Microsoft Windows NT comes on a bootable CD, so you don't need boot diskettes or an MS-DOS hard drive partition before installing it on a new computer.

Some CD-R burning software, such as WinOnCD, allows you to create bootable CDs as images of bootable logical disks. By making such a CD, you can forget about unreliable boot floppies.

Copying CD-ROMs

One of the most common uses for CD-R burners is to copy CD-ROMs. This copying can be done in two ways.

The first method involves creating an image of the source disk as an ISO file and burning this file to the hard disk. In the future, using the disk image file, you can make any number of copies. CD-R burning programs usually allow you to create an image file by reading the tracks of the original disc in sequence. This procedure is much faster than copying the disc file by file.

The second way is to directly copy the original CD-ROM to a blank CD-R. It is useful when you only need one copy of the disk, or you don't have enough hard disk space to accommodate a 650 MB image file. For direct copying, in addition to a CD-R burner, your computer must be equipped with a SCSI-2 CD-ROM reader. The latter circumstance is crucial, since CD-R disc writers are not able to use the widely used IDE CD-ROM readers for direct copying due to insufficient bandwidth of this interface.

When copying CD-ROMs, you should ask if this is allowed by the license agreement. Usually you are allowed to make a backup copy of the CD for personal use, but this is not always the case.

You may come across copy-protected CDs. One of the methods of protection is to write additional data between tracks, which are then checked during the installation or operation of the protected program. Not all CD-R disc burning programs allow you to copy such discs. In particular, the most common Adaptec Easy CD program does not copy additional data. You can use it to copy a protected disk without receiving an error message, but the protected program will not work.

New packet writing technology and CD-UDF format

If the methods of burning CD-Rs just described seem too tedious for you, the volumes have something nice to say. More recently, a new CD-UDF format has been developed that allows (with the appropriate hardware and software) to refer to CD-R and CD-RW discs as regular floppy disks, by their letter designation.

In order for a CD-R writer to be able to create CD-UDF discs, it must be able to work in what is known as packet writing mode.

What it is?

Before the invention of packet writing, the minimum unit of information stored on a CD-R disc in a single session was a track. When using the CD-ROM/XA format, you could add tracks to individual sessions (track-at-once mode), but only complete tracks, not individual parts of them. Batch mode allows you to store even smaller blocks on the disk, as a result of which it is possible to append individual files to a CD-R or CD-RW disc.

Owners of the Microsoft Windows 95 operating system can install the Adaptec DirectCD program, which, using the mentioned packet writing technology, turns a CD-R burner into a regular disk drive. Of course, the device itself must be compatible with the CD-UDF format.

By inserting a CD-R or CD-RW disc into such a device, you can burn files directly to it by dragging and dropping them from folders, the Explorer window, or even saving them using the Save as line of the Windows application's File menu. In addition, you can delete or rename files and directories, as well as overwrite files (Fig. 8).

Rice. 8. Message about the possibility of direct access to the CD-R

Of course, as you work, the amount of free space on the disc is constantly decreasing, since direct overwriting of data on a CD-R disc is not possible. When a file is overwritten, a new version becomes available, while the old one remains in place, taking up free space. There's nothing to be done - a CD-R disc will never perform as well as a magneto-optical disc.

The new technology has a lot of advantages. We will list only a few of them.

Firstly, the procedure for writing information to CD-R discs using Adaptec DirectCD is so simple that it has become accessible even to novice computer users.

Secondly, for just $7-9 you get a 650 MB replacement disk that you can write and re-record individual files on. This is much cheaper than using any other devices such as magneto-optical drives, PD-CDs or JAZZ drives.

Thirdly, by choosing the CD-UDF format, you ensure compatibility with DVD-type high-capacity CD-ROM readers that will be available soon.

Fourth, since the packet size is small, it always fits entirely in the internal buffer of the CD-R burner. Therefore, the buffer underrun problem we discussed above never occurs.

Unfortunately, a disc written in the Adaptec DirectCD format cannot be read on a conventional CD-ROM drive. However, this program can convert it to the Joliet format by adding a title when the disc is ejected (Figure 9). After this procedure, you can access the recorded data under Windows 95 or Windows NT 4.0 by inserting the disc into a CD-ROM drive.

Rice. 9. When ejecting a disc, it is possible to convert its format

Soon there will be CD-ROM and DVD readers that will directly work with CD-R and CD-RW discs prepared by Adaptec DirectCD.

In conclusion, a few tips for those who are going to burn CD-R or CD-RW discs using programs specially designed for this, such as Easy CD Pro.

  • Always test before burning a CD-R disc, especially if you are burning from a virtual disc image. This will avoid a situation where the CD-R disc is corrupted as a result of insufficient disk system performance or an error.
  • Defragment a hard drive containing source files or a disk image file. This will reduce the likelihood of the situation described above occurring.
  • If testing has shown that writing from a virtual disk image is not possible due to insufficient performance of the computer's disk system, try lowering the write speed to single and repeat testing.
  • Before you start burning a CD-R disc, quit all other applications. This also applies to programs to protect the screen from premature burn-in.
  • Never touch the working surface of the CD with your fingers.
  • Do not use ballpoint pens to sign CDs. If you need a CD lettering, make it with a soft felt-tip pen with indelible ink.

Note that when working with CD-UDF discs using the Adaptec DirectCD program, you can ignore all of the above tips except the last two. Because batch mode prevents the writer's buffer from running out of time, you don't need to take special steps to improve disk system performance. You can write files to a CD-UDF disc by copying them from floppy disks, from the network, or by saving them from a running application - there will be no buffer problems.

(C) Frolov A.V., Frolov G.V., 1997, "Hard'n'Soft" magazine

Optical drives

Starting in 1995, a CD-ROM drive began to be included in the basic configuration of a personal computer instead of 5.25-inch drives. The abbreviation CD-ROM stands for Compact Disk Read Only Memory. The principle of operation of this device is to read digital data using a laser beam that is reflected from the surface of the disk. An ordinary CD is used as a storage medium. Digital recording on a CD differs from recording on magnetic discs in high density, so a standard CD has a capacity of about 650-700 MB. Such large volumes are typical for multimedia information (graphics, music, video), so CD-ROM drives are related to multimedia hardware. In addition to multimedia publications (e-books, encyclopedias, music albums, videos, computer games), various system and application software of large volumes (operating systems, office suites, programming systems, etc.) is distributed on CDs.

Compact discs are made of transparent plastic with a diameter of 120 mm. and 1.2 mm thick. A layer of aluminum or gold is sprayed onto the plastic surface. In conditions of mass production, information is recorded on a disc by extrusion on the surface of the track, in the form of a series of depressions. This approach provides a binary record of information. Deepening (pit - pit), surface (land - land). A logical zero can be represented by either a pit or a land. The logical unit is encoded by the transition between the pit and the land. From the center to the edge of the CD, a single track is applied in the form of a spiral 4 microns wide with a 1.4 micron pitch. The disk surface is divided into three regions. The initial (Lead-In) is located in the center of the disk and is read first. It contains the contents of the disk, the address table of all entries, the label of the disk, and other service information. The middle area contains basic information and occupies most of the disk. The end area (Lead-Out) contains the end-of-disk marker.

For stamping, there is a special prototype matrix (master disk) of the future disk, which extrudes tracks on the surface. After stamping, a protective film of transparent varnish is applied to the surface of the disc.

The CD-ROM drive contains:

  • an electric motor that rotates the disk;
  • an optical system consisting of a laser emitter, optical lenses and sensors and designed to read information from the disk surface;
  • a microprocessor that manages the mechanics of the drive, the optical system and decodes the read information into a binary code.

The CD is spun by an electric motor. A beam from a laser emitter is focused onto the surface of the disk using the drive of the optical system. The beam is reflected from the disk surface and fed through the prism to the sensor. The luminous flux is converted into an electrical signal, which enters the microprocessor, where it is analyzed and converted into a binary code.


Key Features of CD-ROM:

  • data transfer rate - measured in multiples of the speed of an audio CD player (150 Kbytes / sec) and characterizes the maximum speed at which the drive transfers data to the computer's RAM, for example, a 2-speed CD-ROM (2x CD-ROM) will read data at 300 KB/s, 50-speed (50x) - 7500 KB/s;
  • access time - the time required to search for information on the disk, measured in milliseconds.

The main disadvantage of standard CD-ROMs is the inability to write data, but CD-R write-once and CD-RW rewrite devices exist.

CD-R drive (CD-Recordable)

Outwardly similar to CD-ROM drives and compatible with them in terms of disc sizes and recording formats. Allows you to perform a one-time write and an unlimited number of reads. Data recording is carried out using special software. The write speed of modern CD-R drives is 4x-8x.

CD-RW drive (CD-ReWritable)

They are used for multiple recording of data, and you can either simply add new information to free space, or completely overwrite the disk with new information (previous data is destroyed). As in the case of CD-R drives, to write data, you need to install special programs in the system, and the recording format is compatible with a regular CD-ROM. The write speed of modern CD-RW drives is 2x-4x.

DVD drive (Digital Video Disk)

Digital video reader. Externally, a DVD-ROM is similar to a regular CD-ROM (diameter - 120 mm, thickness 1.2 mm), but differs from it in that up to 4.7 GB can be recorded on one side of the DVD-ROM, and up to 9.4 GB. In the case of using a two-layer recording scheme, up to 8.5 GB of information can already be placed on one side, respectively, on two sides - about 17 GB. DVDs can be overwritten.

The most important factor hindering the widespread use of CD-R, CD-RW and DVD drives is the high cost of both themselves and removable media.

RELATED ARTICLES