CD-ROM, DVD, CDR and CDRW

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What is a CD-ROM?

CD-ROM is short for Compact Disc-Read Only Memory, which is a type of optical disk capable of storing large amounts of data - up to 680MB per disc. A single CD-ROM has the storage capacity of 470 floppy disks, enough memory to store about 340,000 pages of text.

CD-ROMs require a special machine to record the data, and once recorded, they cannot be erased and filled with new data. To read a CD, you need a CD-ROM drive. Almost all CD-ROMs conform to a standard size and format, so it is usually possible to load any type of CD into any ROM drive. In addition, most CD-ROM drives are capable of playing audio CDs, which share the same technology.

CD-ROMs are particularly well-suited to information that requires large storage capacity. This includes color graphics, sound, and especially video. In recent years, as the prices of CD-ROM drives have decreased, the tools for creating new CD-ROM titles have improved, and the CD-ROM industry has been expanding rapidly. To date, the most popular CD-ROM titles have been computer games and multimedia reference works.

What is a CD-ROM drive?

A CD-ROM drive is a device that can read information from a Compact disc. CD-ROM drives can be either internal, in which case they fit in a drive bay, or external, in which case they are usually connect to the computer ? parallel port or SCSI port. Parallel CD-ROM drives are easier to install, but they have several disadvantages. They are somewhat more expensive than internal drives; they use up the parallel port, which means that you can? use that port for another device such as a printer; and the parallel port itself may not be fast enough to handle all the data pouring through it. SCSI CD-ROM needs an extra SCSI controller board to have it connected. Typically, SCSI controller boards are more expensive than IDE ports.

There are a number of features by which CD-ROM drives are classified, the most important of which is the speed. CD-ROM drives are generally classified as single-speed, double-speed (2X), triple-speed (3X), quadruple-speed (4X), hex-speed (6X) or odo-speed (8X), deca-speed (10x), triple quad-speed (12x), etc. Within these groups, however, there is some variation. Two more precise measurements are the drive? access time and data transfer rate. The seek time, also called the access time, measures how long, on average, it takes the drive to access a particular piece of information on a disc. The data transfer rate measures how much data can be read and sent to the computer in a second.

Aside from speed, another feature by which CD-ROM drives are classified is compatibility with existing standards. If you plan to run CD-ROMs in a Windows environment, you need a drive that conforms to MPC II standard. If you want to view photographs stored on CD-ROM, make sure your drive conforms to the format of a Kodak PhotoCD.

Finally, you should consider how the drive connects to your computer. Most CD-ROMs connect via a SCSI bus. If your computer does not already contain such an interface, you will need to install one. Other CD-ROMs connect to an IDE or Enhanced IDE interface, which is usually the interface used by the hard disk drive.

How do you measure CD-ROM drive performance?

A: The performance of a CD-ROM drive is dependent on two factors: data transfer rate and access time. Data transfer rate refers to the amount of data that a CD-ROM drive can send to a PC in a certain period of time. For example, a CD-ROM with 900 KB/sec transfer rate can read 900K (921,600) bytes of data and transmit it to a PC in one second. (Note that the transfer rate might alter depending on the power of the PC system.) Access time is the time required for a CD-ROM drive to find the desired data on a disc. A shorter access time indicates better performance. When talking about access time, the term "one third stroke" is often used. Stroke refers to the distance from the innermost track to the outer most track of a CD-ROM disk. One third stroke access time is the time it takes for a laser pickup to read data by moving 1/3 stroke over the CD-ROM disk.

How does a drive’s speed affect its performance?

A: A CD-ROM’s speed is measured in terms of its data transfer rate. The data transfer rate for a CD-ROM drive is measured in terms of bytes per second and measures the speed at which the drive can transmit data to the system? memory and CPU for processing. The higher the data transfer rate and the shorter the access time, the better the performance of a drive.

Older single speed drives could transfer data at 150K bytes/second, the same speed as a standard audio drive; but at this speed, images were jumpy and sound output had pops and cracks in it when the drive was used to read a video file such as a Video-CD clip. Multi-speed drives (20X, 24X, 32X, 48x,56x) significantly improve a system’s performance when handling image files. Today’s PCs can handle more in the way of live video clips and animation, and Microsoft Windows offers direct support for multimedia

What is DVD?

A: DVD, short for Digital Versatile Disk, is the newest standard for optical storage, which specifies a disk that is the same size as a standard CD but is able to hold much more information. DVD was developed by an industry consortium of electronics companies led by Toshiba® and Philips®, and it is anticipated the new standard will usher in a new era of growth for multimedia, interactive applications on the PC.

For PC applications, DVD will be used the same way the CD-ROM is used today. The main attraction for PC users is the larger capacity of the DVD disk. The capacity will be 17 gig on a double sided dual layer disk, 8 gig on a single sided dual layer, and 8.4 gig on a CD-R which will only be single layer but could be double or single sided. The PC will also be able to play DVD-Audio and DVD-Video, two standards developed primarily for home electronics devices.
New ROM drives, called DVD-ROM, will be arriving on the market to accommodate the new disk format.

Advances in digital video and audio standards are coinciding with the development of the DVD to create unprecedented multimedia storage capacities. For instance, MPEG-2 video and audio compression will be used to compress still images such as scanned or pictures as well as full motion video. This compression will allow much greater storage than you could attain using a hard drive; for instance, a single-layer, single-sided DVD has enough capacity to hold two hours and 13 minutes of video. Some DVD-ROM drives will have a built-in MPEG-2 chip, and some others will use an MPEG-2 chip installed in the PC.

What are the advantages of DVD-ROM over CD-ROM? : DVD-ROM drives offer several advantages over CD-ROM drives, especially in the area of storage capacity:

Greater capacity: With 4.7 gigabytes of storage capacity on a single layer and 8.4 gigabytes on a dual-layer disc, DVD-ROM offers more than 12 times the capacity of CD-ROM. When information is stored on both sides of the disk a single disk can hold up to 17 gigabytes, which is equal to 26 CD-ROM or 12,000 floppies.

Faster data transfer: A basic DVD-ROM drive offers variable data transfer rate at an average rate of 1, 108 kilobytes per second.

Flexibility: DVD will allow greater use and flexibility of Data Warehousing than ever before possible. One manufacturer has already developed a 100 disk juke box for DVD that can store 800 gig of data in a box only 2’ x 2’.

Better Video: Because DVD-ROM has greater storage capacity and a faster data transfer rate than CD-ROM, it is possible to deliver up to full length movies on a one-sided disk using compression and decompression that yields broadcast quality video and stereo sound tracks for use in Microsoft Windows. Other operating systems supply their own ATAPI CD-ROM device drivers.

What is a CD-R/RW drive?

A: CD-RW is a rewriteable CD utilizing an innovative phase change recording material (Ag-In-Sb-Te). This breakthrough effectively increases data eraseability and recording sensibility, which are two major drawbacks of conventional phase change recording material. During the write operation to a CD-RW, recording switches between the "amorphous" phase (recorded state) with lower reflectivity and the "crystal" phase (erased state) with higher reflectivity according to the temperature rising/falling through laser beam irradiation.

The CD-RW is ideal for personal uses, such as data back-up and making original CDs, because it allows a users to overwrite repeatedly. With CD-R, users can make discs for distribution, create electronic albums of digital camera images, store data that should not be revised or deleted.

What are CLV and CAV?

A: CLV stands for Constant Linear Velocity. To make the CD-ROM drive to achieve higher data transfer rate, the most common way is just simply increasing spindle motor speed. Almost all of CD-ROM makers adopt this way from their early 2X till now. For achieving constant data transfer rate, spindle motor need to run faster at inner track (500rpm for 1X) and slower at outer track (150rpm for 1X). However, when developing 12x or higher speed CD-ROM drives, the problems such as vibration, noise, disc data accessibility, reliability issue,etc. will have to be dealt with, so the way to solve this problem is to slow down the data transfer rate at inner track.

CAV (Constant Angular Velocity), on the other hand, keeps the spindle motor running at the same speed while the CD-ROM is accessing data at inner and outer tracks. In this way, CD-ROM will have lower data transfer rate at inner track and higher transfer rate at outer track. As mentioned above on CLV design, it is getting more and more difficult to overcome those technical issues when CD-ROM's transfer rate is getting higher and higher. For example, spindle motor needs to running at 8000rpm (revolutions per minute) at inner tracks for 16X performance with CLV mode, and it's really too high for current technology as the maximum rpm of hard disk drive is only about 7200rpm. So we believe CAV is more suitable for higher speed CD-ROM design rather than CLV.

How to maintain your CD-R/RW Drive

Typically a CD-R/RW drive will not need much maintenance. Most problems will be prevented if you keep the discs clean. Use a lens-cleaning cloth to slightly wipe away dust on surface and avoid scratching it.