Deciphering DVD and CD

DVD and CD alphabet soup

Did you ever wonder what RW, +R, -R or DVD+RW mean? What is the difference between a DVD and CD? This article explains it all in clear and simple terms.

CD stands for compact disk which is a plastic disk which was originally developed to store music and voice in a digital format. DVD stands for Digital Video Disk which generally looks the same as the CD but can contain much more data and deliver it much faster. The disks use optical disk technology and data is written to the disk and read from it by laser light.

The majority of the suffixes such as R and RW, whether preceded by a plus or a minus, indicate whether the disk is read only, write once and then read only, or rewrite able so that data can be modified or added at will. The pluses or minuses in the name are largely historical and indicate that a particular type of technology was used to allow for the writing or multiple rewriting capability. This used to matter in that some equipment supported one technology and other equipment supported another. The minus was for a type of disk that only Pioneer, Toshiba, Hitachi, Matsushita Electric (Panasonic) equipment would support and Philips, Sony, Hewlett-Packard, Ricoh, Yamaha supported only the plus type of drive. Most current DVD drives can read and write to the disk regardless of the method by which the data is actually stored on the disk so the plus and minus don't matter anymore.

The following table summarizes the meaning of the suffixes;

Suffix Meaning Notes
ROM read only Created by some external agency for use on your computer
R Write once and read many (WORM).

Data that is written to this disk is permanent and the space used for it can't be overwritten or reused. The primary intended use is to write whatever is desired in one session. After this session it can be read but not written to.

The user can write to this disk until it is finalized. It may be readable by some drives before it is finalized but is not readable by all drives until complete. The DVD can be finalized so that it can be read by any drive even after only a very small amount of data has been written to it.
RW Rewrite able The user can rewrite to this disk many times. Data written to it can also be deleted.
RAM Rewrite able Sometimes needs a caddy, which is a special type of tray that holds the disk that is inserted into the drive, to hold the disk
DL Dual layer A double layer of storage material is used on each side of the disk, providing more storage capacity.
Audio Data is stored in a special format (which is not a standard PC file format) which was developed to deliver audio CD or DVD players can play these disks, but they hold much less data than file formats such as MP3 and WMA.
Video Data is stored in a special format which was developed to deliver video This format is intended for feature-length motion pictures that can be played by a DVD player.
BD Blue Ray disk or HD-DVD This is the next level of optical disk storage which will provide huge capacities.

Storage Capacity

CDs can hold 74 to 80 minutes of audio or 700 megabytes of data. DVDs can hold from 4.7 gigabytes of data up to 17 gigabytes depending on the number of sides and the number of layers per side used for storage. Blue Ray disks can hold up to 50 gigabytes, but the drives needed to use them are much more expensive than standard DVD drives. Standard DVD drives will run around $50 while Blue Ray will cost around $600.

CD and DVD Speed

When CD and DVD disk speeds are discussed they are referring to the speed at which information can be stored on the disk. The speed at which the information can be read depends on the particular DVD drive that you are using. Most of the time you will not notice a difference. However, it should be noted that DVD disk speeds are slower than hard disk access.

Detailed information about DVD and CD speed can be found here

DVD Speed Details


CDs and DVDs have long been known as the medium used to deliver commercial software.

DVDs are used for playing music and movies. DVDs have much more bandwidth than VHS tape and can provide a much more robust video and audio experience than these tapes.

They are also used for transfer of data from one computer to another.

Backing up your data is an important step in safeguarding your data. If the data can be taken offsite it provides an extra level of security. Since DVD disks are estimated to have a life span of 25 years and are very portable, they are effective media for storing backups of your data.

DVD and CD Burners

In order to gain the maximum advantage from this technology, one should purchase a drive that supports reading and writing of all formats. These drives are quite cheap and are generally supported by inexpensive or free software such as Nero Express.

Sometimes to save a small amount of money, drives that only write to CD but read or write from DVD are offered. The saving is so minimal that these drives should be avoided.

If you have an older drive check the formats that it supports before purchasing CD and DVD media.

LightScribe is an innovative technology that uses a special disc drive, special media, and label-making software to burn labels directly onto CDs and DVDs. This is a lot more readable and prettier than magic marker scribblings on the CD.

See also Lightscribe Site

With LightScribe enabled DVD drives using LightScribe ready CDs or DVDs (these are standard CDs except that the non recording side of the cd is treated to allow computer generated text and images) the user can make professional looking labels for the disks they create.

DVD Software

There are programs available that allow you to play audio and video content such as Cyberlink PowerDVD. However, Windows Media Player which is supplied with Windows XP can also do this.

DVD and CD burning software such as Nero Express and Roxio Easy DVD Creator provide the tools to record information. They allow you to copy data to the disk and even create a bootable CD or DVD. You can also create audio and video disks that are playable by auto or home players from MP3 or other audio or video file input. DVD and CD copying are also supported unless the source disks are copy protected by content protection schemes. Commercial software, music and video are generally copy protected.

These software tools generally also provide the software necessary to create the LightScribe labels.

For those interested in an exhaustive, in depth discussion of all details of this technology see;

DVD Details 1

DVD Details 2

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