WRITABLE CD-ROM DRIVES

The CD-R Drive

The CD-R (Compact Disk - Recordable) allows you to create (or copy) a CD - either a data disk (CD-ROM disk) or an audio disk. The disk itself is a special type, different from the normal production CD-ROM diskette; it is coated with a photosensitive organic dye that has the same reflective properties as a virgin CD. The laser in a CD-R heats the dye and it changes reflective qualities - that fools a reading CD into thinking there is a pit burned the substrata thus mimicking a production CD. A CD-R is a WORM device (that is: Write Once, Read Many) and is useful as permanent storage of important information. The down side to that is that, once written, a CD-R cannot be changed - if you make a mistake you have, in effect, created an expensive drink coaster.

There are several different types of media available for use in the CD-R, based on size and color. The standard disk is a 650 Mb CD-R (about 74 minutes of recorded music) but there is also a 700 Mb size available (80 minutes of music) which may not be useable with older CD or CD-R drives. The color of the recording surface gives you a hint as to what type of dye is used to record the data; a gold surface will probably have a green dye under it (Cyanine dye) which is pretty much the industry standard. It has a rated lifetime of 10 years and is used by Imation, Memorex, Kodak, BASF, TDK and possibly others. If the surface is silver, it probably has a blue dye (Azo dye) under it. This process was developed by Verbatim and has a rated lifespan of 100 years. This is being used by DataLifePlus, HiVal, Maxwell & TDK - and probably others. The label side of the disk offers you more choices. The conventional surface has places for you to use a marker to write in the information rather than use a label. Then there is the blank, or unbranded, type intended for use with labels and there is a printable surface type intended for use in a special type inkjet CD label printer. Finally, you can buy CD-Rs in bulk (on spindles - the cheapest way) or in jewel cases. Or somewhere in between - packaged in multiples of 5 (usually) and enclosed in some sort of clamshell or holder.

The speed at which a CD-R will write a disk is quite a bit slower than the normal read speed of a CD-ROM drive. Single speed (1x) write drives are obsolete now and a 2x drive is about the slowest you'll see. 4x is considered fast, 8x is high-speed and the fastest is now 12x (or maybe 16x - progress DOES march on!). Single speed (1x) drives transfer data at the rate of 150Kb/sec, so a 650Mb would take a little over 72 minutes to write. Figure in overhead (and for ease of figuring) and we'll call it 80 minutes. So a 2x drive (300Kb/sec transfer rate) would take 40 minutes, a 4x (600Kb/sec) would take 20 minutes, etc.. Unfortunately, the drive speed is not the only factor in how fast you can write a disk. Because a CD-R cannot re-align itself after it starts writing, it must write the entire disk in one smooth operation. That means the entire computer (software and hardware) must reliably transfer data to the CD-R at (at least) the rate at which it is writing. The CD-R software generally creates a buffer on your hard disk to temporarily store the data it transfers to the CD-R, but if that should run dry you will get a 'buffer underrun error' and the CD will be ruined. Reliably creating CD-Rs is a subject worthy of study and requires going deeper into data transfer than I am willing to go here. I'll just say that if you get buffer underrun errors, try slowing down your write rate (from 4x to 2x, for example) and, if possible, understanding SCSI versus IDE data transfer BEFORE you buy could save a lot of headaches down the road a bit.

The final factor in creating CDs is the software. A normal drive, either a CD-ROM drive or a hard drive, usually has all the software it needs already built-in to the operating system; not so the CD-R (or CD-RW). The drivers and disk mastering software are unique to each different type drive and you must have them in order to use the drive. If you have a disk mastering program such as Adaptec's Easy CD Creator (or DirectCD) or something similar, you probably have the drivers you need to install your CD-R drive. If not, you may be able to download the drivers directly from the drive manufacturers web site, but you'll still need some type of disk mastering program in order to create disks.

The CD-RW Drive

The CD-RW (Compact Disk - ReWritable) drive uses a different type (and slightly more expensive) disk to allow you to erase and re-write data up to 1,000 times. The photosensitive dye used in a CD-RW disk is Ag-In-Sb-Te (silver-indium-antimony-tellurium), an alloy that, in it's original state, has a polycrystaline structure that makes it reflective. When the CD-RW writes to the disk, it used its laser at the highest power setting which heats the alloy to 500 to 700 degrees Celcius, causing it to liquify. In this liquid state, it loses its polycrystaline structure and solidifies in a non-reflective state as it cools. The erase function is caused by firing the laser at a medium setting, which heats the alloy to 200 degrees Celcius and causes it to go back to its polycrystalline (reflective) state.

A CD-RW disk has a much lower reflective capability than a comprable CD-R disk and, because of that, may not be able to be read by some older CD-ROM drives (drives below 24x, usually) and many CD-R drives. If your drive has "Multi-read" capabilities, it probably won't have any problem reading a CD-RW created disk. Since all CD-RW drives have CD-R capabilities, it's probably best to create CD-R disks if you are sending the disk to someone else and use the CD-RW mode for internal backups or other personal uses.

Everything in the above article about CD-R data transfer and software is true also for the CD-RW drives.

See also CD-ROM Drives

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