CD-ROM Technology
CD-ROM (Compact Disc Read Only Memory) technology is an outgrowth of audio compact disc technology, which was introduced in the early 1980s. Based on the same basic disc, a CD-ROM can store up to 650 MB of computer data. This data can be text, spreadsheets, digital images, video or audio files, or any other type of information you might find on your hard disk drive. A CD-ROM is a "read-only" disc-the data is pressed into the disc just like the grooves of an LP record. A CD-ROM drive uses a laser to "read" the data recorded on a CD-ROM disc, then translates it into bits and bytes that eventually make up the data files you use on your computer.

CD-ROM Compatibility
The entire CD technology family conforms to a set of international standards, commonly referred to as "color books," to ensure all CDs are compatible with other CD players -ROM drives. Even though the basic construction of every CD is the same, their "formats" vary by use.

The RED BOOK defines a CD Audio standard for the common audio CDs you buy at the store. YELLOW BOOK defines a CD-ROM standard that specifies how data is arranged on a CD-ROM. The Yellow Book has sub-books that define CD-XA discs. The GREEN BOOK defines a Compact Disc Interactive (CD-I) standard for a special multimedia format that can be played on a set-top player attached to a television set. The WHITE BOOK defines a Video CD standard for MPEG-1 video discs played on a set-top player attached to a television set. You can buy full length Video CD movies, however, the quality isn't quite as good as DVD. The BLUE BOOK defines a CD Extra standard that specifies a way to put both CD audio tracks and computer data on the same disc, but in different sessions, or recording areas. The audio session is recorded first, then the data session. This way, when the disc is played in a CD player, only the audio tracks can be "seen" and played. When the same disc is placed in a standard multi-session CD-ROM drive, the audio tracks and the data track will be visible. The ORANGE BOOK defines a CD-R -RW standard that specifies how the above "formats" are stored on CD-R -RW discs that you can record. The Orange Book is broken down into 3 parts, one for CD-MO (a disc type that never took off), one for CD-R (called Orange Book part II), and one for CD-RW (called Orange Book part III). These books define the characteristics of the recorder and blank discs, and how to perform the recording.

One of the unique features of a CD-ROM is its ISO9660 file system, sometimes called the "logical format." ISO9660 defines the format in which files and folders are arranged on a CD-ROM so a computer can locate them. The system is cross-platform compatible, so that standard CD-ROMs can be read by PCs, Macintosh and even UNIX systems. Of course, application programs are designed for specific types of computer platforms, but the actual files and folders are visible under other platforms. "Hybrid" CD-ROM discs combine ISO9660 with another native file system, such as the Macintosh or UNIX operating systems. These discs contain native PC and native Macintosh (or UNIX) sections, and display only the files for the type of computer reading the disc.

Today, CD-ROM discs are used to distribute software and information on a large scale. Since most PCs today have CD-ROM drives built in, distributing application programs and data is a snap. In the past, an application program that took 20 floppy disks to install can easily be placed on a single CD-ROM disc. The user simply starts the installation process and can walk away-no more swapping floppy disks! Because CD-ROM discs are inexpensive to produce, hold up to 650 MB of data and have wide compatibility with popular computer systems, they are ideal for distributing large amounts of data or applications to computer users.

CD Recordable (CD-R) Technology
Compact Disc Recordable technology was developed in the early 1990s as a tool for software developers who wanted to prototype discs before stamping thousands of them. The first CD recorders cost over $100,000 and were as big as washing machines. The blank discs cost more than $100. Today, an entry-level CD-R drive costs under $300, looks just like a CD-ROM drive and the blank CD-R discs cost only a few dollars. CD-R discs can hold up to 650MB of computer data, or up to 74 minutes of quality CD music.

CD-R is a "write once" technology-once the data is recorded, it is permanent and cannot be changed or erased. The data from the computer is broken down into "1s" and "0s" and burned into the recording layer of the CD-R disc as dark spots. Data is read back from a CD-R disc just like a regular CD-ROM. However, CD-R discs look different than regular CDs. They are usually gold on the label side, while the other side might be green or gold, depending on the recording material. Once CD-R discs are recorded, they can be read by any standard CD-ROM drive or CD player, because the recorded disc "looks" the same as a stamped CD to the player. Data can be added to CD-R discs in "sessions", but not erased.

CD-R Compatibility
The ISO9660 file system is typically used to record a CD-ROM, in order to ensure compatibility with multiple CD-ROM drives and operating systems. However, a newer file system called Universal Disc Format (UDF), a more flexible and efficient format for recording CDs, is also becoming popular. ISO9660 was designed for read-only discs and is cross compatible, but not ideal for writing files and folders one at a time. Of course, the other popular format is CD audio, which is universal for playing audio discs in any CD player, CD-ROM or even DVD-ROM drive.

CD Recording Software
CD recording software falls into two basic categories: Pre-mastering or Drive Letter Access (DLA). Pre-mastering software typically creates the basic CD formats, such as CD audio and CD-ROM. All the files/folders or audio tracks get added to the application software and recorded at once. Audio CDs must be recorded all at one time as a "single session", but CD-ROM discs can have several recorded "sessions", resulting in a "multi-session" disc. Sony HotBurn is a good example of Pre-mastering software. Drive Letter Access (sometimes referred to as packet writing) software formats the disc much like a floppy disk, so that individual files and folders can then be dragged from any source to the drive letter of the disc. Files can even be saved directly from an application to this kind of disc, since it behaves just like a floppy or hard disk. However, when recording on CD-R discs, the files can be "virtually" deleted while the actual files are still present on the disc. Also, most Drive Letter Access software records the data in the newer UDF file system for maximum flexibility. Sony abCD is a good example of Drive Letter Access software.

Since CD-R discs can hold up to 650 MB of permanent data and can be read back by standard CD-ROM drives, they are ideal for applications that involve distributing large files to small groups, or for applications such as data archiving, where the permanence of write once technology is necessary. Many medical, legal and government organizations require this kind of permanent storage, and are ideal applications for CD-R technology. Music studios can also use CD-R discs to give clients a cut of an album on the final medium the music will be distributed on, instead of on a cassette tape. Since the discs are low cost, they provide a cost-effective means for distributing large files.

CD-ReWritable (CD-RW) Technology
Compact Disc ReWritable technology is a recent addition to the CD family and a natural extension of CD-Recordable technology. As its name suggests, a CD-RW disc can be erased and re-written, in the same way a floppy disk can be erased or re-formatted. Just like CD-R discs, CD-RW discs hold up to 650 MB of data or 74 minutes of CD quality music. CD-RW discs are silver on the label side, just like a stamped CD, however, the recording side is a dark gray color. CD-RW uses a technology called "phase change" to record a "mark" on the disc that simulates a pit. This is accomplished by heating the spot to be recorded to a specific temperature very quickly. The mark can be changed by heating the spot again to a lower temperature, causing it to re-crystallize. This cycle can happen about 1,000 times on current CD-RW media.

CD-RW Compatibility
While CD-RW discs can be erased and re-written, they cannot be read by all standard CD-ROM drives and CD players. The phase change recording material of a CD-RW disc isn't as reflective as a stamped disc or even a CD-R disc. As a result, the recorded CD-RW discs are only readable in CD-ROM drives that advertise CD-RW compatibility, or that conform to the new Multi-Read specification. While most new CD-ROM drives sold today are compatible with CD-RW discs, there are many drives already installed in computers that cannot read these discs. However, CD-RW discs were not designed to replace CD-R, in fact they are complementary technologies.

A CD-ReWritable recorder is a multi-function drive. It can record a CD-RW or a CD-R disc. Since CD-RW discs cost more than CD-R discs, and are not as compatible with CD-ROM drives installed in the field, CD-R discs remain the best medium for distributing large files and data. CD-RW, because it is rewritable, is better for general data storage (personal file storage) or daily back ups, whenever data is frequently updated. CD-RW is also an ideal prototyping medium for making a CD-ROM that will eventually be stamped. If a problem is found in the program, a change can be made and the CD-RW disc re-burned with the new information. When the project is done, a CD-R disc can be recorded as a master. CD-R -RW work together to meet all your information management needs.

CD-RW Recording Software
The same CD recording software used to record a CD-R disc can be used to record a CD-RW disc. All the same disc formats apply to CD-RW. You can record music onto a CD-RW disc, however, you probably wouldn't be able to play it in your car or home stereo. For that application, use a CD-R disc in the recorder. Pre-mastering software that supports CD-RW discs usually has an option to erase or "blank" a CD-RW disc. This is necessary, as a CD-RW disc recorded with this type of software looks like a regular CD-ROM or CD Audio disc to the CD recorder once it has been written. Drive Letter Access software can directly overwrite a file with CD-RW media so you should never have to erase this kind of disc.

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