Optical Disk and Drives

Optical disks can store information at much higher densities than magnetic disks. Thus, they are ideal for multimedia applications where images, animation and sound occupy a lot of disk space. Besides, they are not affected by magnetic fields. This means that they are secure and stable, e.g. they can be transported through airport metal detectors without damaging the data. However, optical drives are slower than hard drives. While there are hard drives with an average access time of 8 ms, most CD-ROM drives have an access time of 150 to 200 ms.

There are various types of optical drives:

CD-ROM systems offer everything, from shareware programs to dictionaries and encyclopaedias, from multimedia databases to 3-D games. A lot of institutions have discovered that CD-ROM is the most economical way of sharing information. In fact, one CD-ROM disk (700 MB) can replace 300,000 pages of text (about 500 floppies), which represents a lot of savings in distributing materials and corporate databases. In addition, CD-ROM drives can play music CDs while you work. Yet CD-ROM technology has one disadvantage: you cannot write anything onto a CD-ROM disk. You can only ‘read’ it, like a book.

CD-Recorders come in two different forms: CD-R and CD-RW. CD-R machines record on CD-R (even by portions of 2 KB as many times as you like, but not more than the disk capacity is) disks, allowing you to create and duplicate CDs. They are used to back up hard disks or to distribute and archive information. In fact, these systems are the modern version of old WORM (write once, read many) disks. CD-RW machines hold CD-RW (rewritable) disks that you can erase and re-use, just as you would do with a hard disk.

The future of optical storage is called DVD (digital versatile disk). A DVD-ROM can hold 17 GB, about 25 times an ordinary CD-ROM. For this reason, it can store a large amount of multimedia software and complete Hollywood movies in different languages. They can also play music CDs and CD-ROMs. However, DVD-ROMs are ‘read-only’ devices. To avoid this limitation, companies also produce DVD rewritable drives.

DVDs can be of single layer and double layer. Double layer DVD means that such disk has recording surfaces on each side. Certainly, such disks may contain two times more information than (approximately 9MB). DVDs are made in two form-factors: 12 cm (4.7”) and 8 cm (3.1”). 8cm DVD are usually called mini-DVD and may contain information not more than 1.46 GB. Laser with the wavelength of 650 or 635 nm is used for recording.

DVD-R is a DVD recordable format. The original standard developed by Pioneer was 3.95 GB (3.68 GB). Pioneer has also developed an 8.54 GB double layer version, which appeared on the market in 2005. Data on a DVD-R cannot be changed, whereas a DVD-RW (DVD-rewritable) can be rewritten multiple (1000+) times. DVD-R(W) is one of three competing industry standard DVD recordable formats; the others are DVD+R(W) and DVD-RAM.

A DVD+R is a once-writable optical disc with 4.7 GB (4.4 GB) of storage capacity (more precisely, 2295104 sectors of 2048 bytes each). It has slightly less storage capacity than the DVD-R (4.4 GB). The format was developed by a coalition of corporations, known as the DVD+RW Alliance, in mid 2002. Since the DVD+R format is a competing format to the DVD-R format, which is developed by the DVD Forum, it has not been approved by the DVD Forum, which claims that the DVD+R format is not an official DVD format.

A DVD-RW is a rewritable optical disc with equal storage capacity to a DVD-R, typically 4.7 GB. The format was developed by Pioneer in November 1999 and has been approved by the DVD Forum. The primary advantage of DVD-RW over DVD-R is the ability to erase and rewrite to a DVD-RW disc.

DVD+RW is the name of a standard for optical discs: one of several types of DVD, which hold up to about 4.7GB per disc (and are used for storing films, music or other data. DVD+RW supports random write access, which means that data can be added and removed without erasing the whole disc and starting over (up to about 1000 times). With suitable support from the operating system, DVD+RW media can thus be treated like a large floppy disk, in contrast to DVD-RW which must be erased before re-writing can take place.

DVD±RW is a multipurpose (multiformat) DVD dirve. DVD±R is not a separate DVD format, but rather is a shorthand term for a DVD drive that can accept both of the common recordable DVD formats. Likewise, DVD±RW handles both common rewritable disc types (but not usually DVD-RAM).

DVD-RAM (DVD-Random Access Memory) is a disc specification presented in 1996 by the DVD Forum, which specifies rewritable DVD-RAM media and the appropriate DVD writers. DVD-RAM media have been used in computers as well as camcorders and personal video recorders since 1998. DVD-RAM is considered a highly reliable format, as the discs have built-in error control and a defect management system. Therefore, DVD-RAM is perceived to be better than the other DVD technologies for traditional computer usage tasks such as general data storage, backup and archival, though the Mt. Rainier standard for DVD+RW somewhat lessens the DVD-RAM format's perceived advantage. Curiously, DVD-RAM has a larger presence in camcorders and set-top boxes than in computers, although the DVD-RAM’s popularity in these devices can be explained by the fact that it is very easily written to and erased, which for example allows extensive in-camera editing.

Magneto-optical (MO) drives use both a laser and an electromagnet to record information. Consequently, MO disks are rewritable, i.e. they can be written to, erased, and then written again. They usually come in two formats: 1) 5.25" cartridges can hold more than 2 GB; 2) 3.5" floptical disks have a capacity of 230 to 640 MB. They are ideal for back-up and portable mass storage.

6. Read the text again and summarize in the table the most relevant information.

	Technical specifications	Use
CD-ROM
CD-Recorder
DVD
Magneto-optical

7. Answer the questions.

1. What is ideal for multimedia applications? 2. What does it mean that optical disks are not affected by magnetic fields? 3. Are optical drives faster than hard drives? 4. What is CD-ROM? 5. How many times can you record on CD-R disk? 6. What types of DVDs do you know? 7. What is mini-DVD? 8. When was the DVD+R format developed? 9. What can you say about DVD-RAM? 10. What are the rewritable disks?

8. Fill the gaps with correct words or phrases.

1. CD-ROM systems offer everything, from shareware programs to ___________________, from multimedia databases to ________________.

2. ___________________ that CD-ROM is the most economical way of sharing information.

3. CD-ROM drives ____________________ while you work.

4. CD-ROM technology has one disadvantage: _________________________.

5. ___________________ is called DVD (digital versatile disk).

6. Double layer DVD means _____________________ on each side.

7. ___________________ is a once-writable optical disc with 4.7 GB (4.4 GB) of storage capacity.

8. ___________________ is the ability to erase and rewrite to a DVD-RW disc.

9. ___________________, DVD+RW media can thus be treated like a large floppy disk, in contrast to DVD-RW which ________________________.

10. DVD-RAM is perceived to be better than ___________________ for traditional computer usage tasks such as ___________________________.

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