Write Once:

The optical disks that you can record on your own computer are CD-R, DVD-R, and DVD+R discs, called writable or recordable disks. The metal and data layers are separate.  The metal layer can be gold, silver, or a silver alloy.

Go for the Gold:  Gold layers are best because gold does not corrode. Naturally, the best is more expensive. Sulfur dioxide can seep in and corrode silver over time.

The data layer is an organic dye that the writing laser changes. Once the laser modifies the dye, it cannot be changed again. Write Once! Ultraviolet light and heat can degrade the organic dye. Manufacturers say that these disks have a shelf-life of 5 - 10 years before they are used for recording. There is no testing yet about how long the data will last after you record it.

A writable disk is useful as a backup medium when you need long-term storage of your data. It is less efficient for data that changes often since you must make a new recording each time you save your data. Pricing of the disks will be important to your decision to use writable disks.

Rewrite:

An option for backup storage of changing data is rewritable disks, CD-RW, DVD-RW, DVD+RW, DVD+RAM.

The data layer for these disks uses a phase-changing metal alloy film. This film can be melted_[54] by the laser's heat to level out the marks made by the laser and then lasered again to record new data.

In theory you can erase and write on these disks as many as 1000 times, for CD-RW, and even 100,000 times for the DVD-RW types.

Advantages of Optical Disks

1. Physical: An optical disk is much sturdier_[55] than tape or a floppy disk. It is physically harder to break or melt or warp.

2. Delicacy:_[56] It is not sensitive to being touched, though it can get too dirty or scratched to be read. It can be cleaned!

3. Magnetic: It is entirely unaffected by magnetic fields.

4. Capacity: Optical disks hold much more data than floppy disks.

Plus, the non-data side of the disk can have a pretty label!

For software providers, an optical disk is a great way to store the software and data that they want to distribute or sell.

Disadvantages of Optical Disks

1. Cost: The main disadvantage has been cost.

The cost of a CD-RW drive has dropped drastically_[57] and quickly. In 1995 such a drive was around $3000. In the summer of 1997 CD-RW drives were down to just under $1000. In March 2003 a CD-RW that will read at 40X speed, write on CD-R media at 40X speed,  and write on re-writable media at 12X,  can be bought for under $100 US!!

The cost of disks can add up, too. Recordable disks (one time only) cost about $.30 US each (March 2003). Re-writable disks cost about $.64 to $.85 each.

So for commercial use, the read/write drives are quite cost effective. For personal use, they are available, but may not be quite yet cheap enough to use for data storage for everyone.

2. Duplication: It is not as easy to copy an optical disk as it is a floppy disk. You need the software and hardware for writing disks! (This is an advantage as far as commercial software providers are concerned!) This is balanced by the fact that it is not as necessary to have extra copies since the disk is so much sturdier than other media.