CDROM DRIVE

CD-ROM drive: Pronounced see-dee-rom. Short for Compact Disc-Read-Only Memory, a type of optical disk capable of storing large amounts of data -- up to 1GB, although the most common size is 750MB (megabytes).

CD-ROM s are stamped by the vendor, and once stamped, they cannot be erased and filled with new data. To read a CD, you need a CD-ROM player. All CD-ROMs conform to a standard size and format, so you can load any type of CD-ROM into any CD-ROM player. In addition, CD-ROM players are capable of playing audio CDs, which share the same technology that support color, graphics, sound, and especially video.

CD-ROM s are read using CD-ROM drives and written with CD recorders (often referred to as "burners"). CD-ROM drives—now almost-universal on personal computers—may be connected to the computer via an IDE (ATA) interface, a SCSI interface or a proprietary interface, such as the Panasonic CD interface. Most CD-ROM drives can also play audio CDs and Video CDs with the right software.

CD-ROM s are written and read using hills and valleys on the disc that are microscopic. The light/dark and dark/light (pit edge) transitions are translated into 1 bits, the areas with no transitions are translated into 0 bits[citation needed]. The CD-ROM reads the hills and valleys by using laser reflecting off of the CD-ROM into a detector that can sense the difference in reflection.

CD-ROM drives are rated with a speed factor relative to music CDs: 1x or 1-speed which gives a data transfer rate of 150 kilobytes per second in the most common data format. For example, an 8x CD-ROM data transfer rate would be 1.2 megabytes per second. Above 12x speed, there are problems with vibration and heat. Constant angular velocity (CAV) drives give speeds up to 20x but due to the nature of CAV the actual throughput increase over 12x is less than 20/12. 20x was thought to be the maximum speed due to mechanical constraints until

Samsung Electronics introduced the SCR-3230, a 32x CD-ROM drive which uses a ball bearing system to balance the spinning disc in the drive to reduce vibration and noise. As of 2004, the fastest transfer rate commonly available is about 52x or 7.62 megabytes per second, though this is only when reading information from the outer parts of a disc.

Future speed increases based simply upon spinning the disc faster are particularly limited by the strength of polycarbonate plastic used in CD manufacturing, though improvements can still be obtained by the use of multiple laser pickups as demonstrated by the Kenwood TrueX 72x which uses seven laser beams and a rotation speed of approximately 10x.

CD-Recordable drives are often sold with three different speed ratings, one speed for write-once operations, one for re-write operations, and one for read-only operations. The speeds are typically listed in that order; ie a 12x/10x/32x CD drive can, CPU and media-permitting, write to CD-R disks at 12x speed (1.76 megabytes/s), write to CD-RW discs at 10x speed (1.46 megabytes/s), and read from CD discs at 32x speed (4.69 megabytes/s).
The 1x speed rating for CDs (150 kilobytes/s) is not to be confused with the 1x speed rating for DVDs (1.32 megabytes/s).

Some of the initial versions of CD Drives had a mechanism different from the tray or slot loaders of modern day drives. They could read CDs only when they were inserted in special cartridges. The "CD Caddy" resembled the floppy disk because of its protective casing. It never became popular, however, possibly because it would be cheaper for manufacturers to produce CDs without cartridges (CD caddies, although resembling ordinary jewel cases, were probably more expensive to produce because of their additional metal components and, unlike jewel cases, they could not hold a printed booklet or inlay cards).

Furthermore, distributors using the cartridge format would still have to offer loose CDs for owners of non-caddy drives in order not to lose part of the market, whereas caddy owners could still play loose CDs by loading them into an openable cartridge which was then inserted into the drive (this of course defeated their entire purpose and was more fiddly than loading a disc into an ordinary drive).

Some might argue that caddies would be a good idea given the somewhat fragile nature of some cheaply produced modern CDs - whereas some early CDs had the recording medium sandwiched between two layers of plastic, offering good protection from scratches, some modern discs have a single layer of plastic with the medium stuck to one side, offering comparatively little protection from scratches to the top side of the disc, other than via the printed label paint - some particularly cheap recordable discs have even been known to have their recording layer peel away from the plastic substrate entirely, and of course become useless.

To use a CD-ROM disk in the drive, press the button (should be the only one visible) on the front of the drive to eject the tray, insert the disk so it lines up with the indent in the tray, and either push the tray back in or press the button again. Each of these closing methods are effective and, contrary to a common misconception, giving the tray a push to begin the retracting process does no damage to the drive. Over time retracting does affect the performance of a disc drive, but only on certain models that are not dependable.

There are several formats used for CD-ROM data: the Rainbow Books, which include the Green Book, White Book and Yellow Book CD-ROM. ISO 9660 defines the standard file system of a CD-ROM, although it is due to be replaced by ISO 13490. UDF format is used on user-writable CD-R and CD-RW discs that are intended to be extended or overwritten. The bootable CD specification, to make a CD emulate a hard disk or floppy, is called El Torito (apparently named after the restaurant chain).
Informative CD-ROMs may contain links to webpages with additional information. To keep them up to date these are sometimes indirect: they link to webpages maintained by the producer of the CD-ROM which contain the links to external webpages.