CD-ROM The first born among the various optical media is the “old” CD-ROM, limited to a maximum capacity of about 750 Mb .
The most recent DVD format, just to give you an idea, instead allows you to store up to 8.5 GB of data in each disk .
The origin of the CD dates back to 1979 , its genesis is due to the search for an efficient system information storage . The intention was to create a mount that can accommodate sound information expressed in binary (1 and 0) . Thanks to the use of the laser has been possible to give life to the Compact Disc. CDs intended for a Use with your computer, mass-produced and on which you can not write , are known as CD-ROM ( ROM is stands for Read Only Memory , a read only memory ) .
All the latest computer have at least a unit of writing able to write CD-R discs . Most of the media currently on the market can hold up 400 images in high resolution , or approximately 140 songs of average length . The discs are characterized by the initials CD -R ( where R is stands for recordable or recordable ) can be written once and the contents are not can no longer be canceled. In addition to storing data personal computer with a CD-R can then create an Audio CD with 74 or 80 minutes of music , usable on most players CD present in the hi-fi . The next step of the designers was therefore the creation of the format CD -RW (CD- ReWritable ) commonly known as CD rewritable media on which you can engrave the data multiple times.
These discs offer the same capacity of a normal CD- R , with the difference that cost a little ‘ more. Most recorders currently in circulation can write to both CD-R and CD -RW discs. CD-RW discs have a shorter duration CD-R .
It is difficult to indicate a period precise time , however , the exact duration depends on the number of times in which they are written data and certain environmental conditions as : humidity, temperature and exposure to light.
The manufacturers claim about a thousand rewrites possible on the CD -RW but in reality the real ones are many less . Within the family of the CD -ROM it is Also worth noting less used formats such as VCD ( Video CD) and SVCD ( Super Video CD ), which contain audio and video files . These types of CD -ROM functions have similar functions to those of the DVD also if they offer a lower quality and , between the two, SVCD delivers performance slightly higher than those of the VCD . these discs can be produced and used with most PCs and on many DVD players.
They are part of the family CD also CD-Text and CD + G. The CD- Text is a particular format of CD -Audio that on some CD players of hi-fi equipment allows see the text for each track. The CD + G is instead a particular CD -Audio information Graphics that require the use of a special player ; is often used to produce the discs from karaoke .
The DVD format has become famous as DVD (Digital Video Disc) is born in the early 90s when many manufacturers have begun to develop a more capacious disk of the traditional CD-ROM. In a second time , thanks to its success and widespread use with your personal computer the meaning of the “V” in the acronym DVD is changed to ” Versatile” . No one noticed it though, because the acronym had become famous and commonly used .
The normal DVD can hold 4.7 GB of data ( enough for about 2000 high quality images ) , so they are six times more capacious than the CD -ROM drive. This capability can be
extended further through some tricks . For example , a disk may have more than one data layer on the surface , reaching almost to double the amount of data stored ( up to 8.5 Gb, sufficient for a two hour film with very high quality, or about eighteen hours compressed video ) . This format is called Double Layer , or sometimes dual layer. DVD discs can also be double-sided (Double sided in English ) ; accordingly , a disc Double sided and double layer can contain 17 Gb of data. The double-sided discs , however, you can easily damage and, consequently, are rarely used .
Some films or television series are available on the market on these particular double-sided discs , but to play the second side must physically turn them into the player. DVD discs already written and designed to use with the PC , are known with the name of the DVD-ROM (since it is not possible to overwrite the contents ) . Regarding the recordable DVD , there are instead two main versions : the DVD-R and DVD + R. These variants have been developed by different companies and are not compatible with each other .
In any case, most modern DVD Writer can read and write to both types of disc . If you have a larger unit dated before buying discs should check which version is supported. Both variants (DVD- R and DVD + R) can store 4.7 GB of data , similar to their equivalents rewritable DVD + RW and DVD-RW. These two formats I agree to erase and rewrite data several times , but not indefinitely as we tend to mistakenly believe.
The number of records supported , declared by the manufacturer , is about a thousand : a number equal to that of re-writable CDs although the actual number of entries is less possible . Most modern writing drive can write to all four formats described : DVD + R, DVD -R, DVD + RW and DVD-RW.
Double layer discs with a capacity of up to 8.5 Gb, until recently were used only for movies ( the ones you buy in the store ) , but today most of the new DVD Writer can write disc Double layer DVD + R and DVD-R. These units are not writing much more expensive than other models and can be used for saving data as an alternative to external disks that still have a rather high price .
Finally, we must point out that the disk write takes longer since the support may contain a double amount of data .
DVD- RAM ( RAM means Random Access Memory , a slang term for a storage space in which you can write multiple times) are not widely used on PCs , on the other hand can be found with some frequency as a support election for video recorders and video cameras equipped with DVD recorder. Usually the DVD-RAM adopt a plastic housing that has the purpose of protecting the surface of the disc. Some units of writing for PC are able to write to DVD-RAM discs , but most scanners on the market, can neither write nor read such media. The optical drive specifically designed for the DVD -RAM , even if it is aesthetically similar to the other readers, do not eject the media tray on the classic , but on a charger .
This type of player also supports previous formats: CD -Audio , CD -ROM, CD -R, CD -RW, and photo CDs .
Finally, we must mention the Kodak Picture CD : A CD containing the photos in digital format along with the features you need to enlarge , crop , sharing and printing .