Neon-komputadór

CD Drive

A CD Drive reads - and some cases writes - to an optical medium storage (up to 682 megabytes) unit called a compact disk or CD. A CD is a 118 millimetre polycarbon disc coated with a metallic strata (usually aluminum alloy) and another polycarbon layer. The top of the disc is usually labeled as all reading occurs from the bottom - CDs are single sided. The metallic strata is where the CD-Drive reads the information on the CD. A low-powered laser strikes the strata and a light receptor determines whether it is reflected or absent. This binary state is transformed into data or sound. CDs have a track density of about 7,100 tracks per centimetre and a transfer rate in multiples of 150kilobytes per second, depending on the location of the data on the CD and the speed of the CD drive.

CD's are not as fast nor can they hold as much information as a magnetic fixed hard disk system. They have become very popular however as a means of storing data for offline and archival purposes. With the increased development of CD-RW (compact disc re-writable) drives and discs it also seems probable that in the near future such a system with replace the floppy disk drive - after all, one single CD holds as much data as more than 450 floppy disks.

Many users think that because they are hard, CDs require less care. This is not the case - as an optical medium, scratches, fingerprints etc. can make a CD difficult to read. Dirt and dust in the CD Drive can clog up the mechanisms and collect on the lens leading to complete failure. CDs should be handled carefully and both CDs and CD Drives should be cleaned regularly with a clean cloth and an alcohol-based cleaner. Clean the disk (carefully!) from the center to the edge, so that if any scratches arise from cleaning at least they'll be across the tracks rather than along them.

When using a CD Writer some care should be taken, as CD write failures are quite annoying and time consuming, not to mention a waste of money. A good quality CD dye and brand is recommended (unless the CD is being used for temporary purposes). Gold-green is forgiving of read/write errors whereas Silver-blue is recommended for archives. The former is produced by Imitation, Memorex, Kopdal, BASF and TDK and the latter by Verbatim, DataLifePlus, HiVal, Maxell and TDK. SCSI CD Writers are significantly more reliable. If you have the time set the writing process to a lower time and set the buffer to a high value (1 megabyte or more). It's also a very good idea to let the computer write the CD as a single job to ensure a steady flow of data. So let the write process begin and leave your computer running.

CD-RW (CD-ReWritable Drives) have pretty well replaced CD-R Drives in most advanced nations and corporate settings. Technically, CD-RW disks are supposed to capable of being rewritten up to a 1,000 times without problems. However, the lower reflectivity of the disc means that many standard CD-ROM and CD-R drives cannot actually read CD-RW discs (isn't that annoying?). Fortunately CD-RW drives can write to standard CD-R discs and read standard CD-ROMs. So obviously CD-RW drives are the preferred technology.

The future of optical media is undoubtedly the DVD (Digital Versatile Disk), which has an initial storage of 4.7 gigabytes on a single-sided disc the same size as a Compact Disc. Current models of DVD are also compatible with 8.5 gigabyte dual-layer discs and double-sided DVD's that will store 17 gigabytes. DVD is evolving and as such, there are few standards apart from the DVD reading technology. Recordable DVDs, for example, come in two general formats DVD-R and DVD-RAM, but DVD-RAM discs cannot be read by many standard DVD-ROM drives because of differences in reflectivity and the data format. DVD-RW (DVD-rewritable) was released in late 1999 and these drives can read and write to DVD-R discs.

If at all possible an optical media drive should have the Multiread or even better the Multiread2 specifications. The former is a drive that can read the following discs: CD-Audio, CD-ROM, CD-Recordable and CD-Rewritable. Multiread2 can read all of the previous plus DVD-ROM, DVD-Video, DVD-Audio and DVD-RAM.

The various types of CD Drives are connected to a SCSI or IDE/APATI interface, the parallel port or USB (Universal Serial Bus). The former consist of both slot and tray loading, whereas the latter are all tray loading drives. Whilst slot loading drives appear more "high tech", they are more difficult to repair. There is also the regrettable tendency for users to try to force floppy disks into the CD ROM slot which is annoying to repair and has a high probability of causing significant damage to the CD Drive.