A disc that can contain data is called "media," or more often, just a "disc." A machine that can read and/or write on media is called a "drive."

When you buy blank CDs or DVDs for recording, they may be labeled "for audio," "for video," or "for data." However, all blank optical media can be used for any purpose. The special discs for "audio" or "video" are just priced higher, but they're axactly the same as for data. For blank CDs, just get the cheapest ones. For blank DVDs, try to only buy the name-brand ones (the companies you recognize, like Sony, TDK, etc.), as the "off-brand" DVDs often fail.

Recording Categories

There are some special terms used for optical discs. These combinations of letters can be extremely confusing. Let's see if we can organize them. First, there are terms for the recording status of the disc:

For a very long time, most computers have had a CD-ROM drive, which can only read CDs. Just about all computers today have a CD drive which can read and write CDs--this is called a CD-R/RW (CD-Recordable/ReWritable).

Most computers also have a DVD-ROM, usually in the same drive as the CD-R/RW. DVD-ROM can read DVDs, but cannot write to them. The optical drive which has both CD-R/RW and DVD-ROM is often called a "combo drive."

If you want to be able to write on blank DVDs, you will want a DVD-R/RW drive. Writing on DVDs is useful mostly in creating videos or in storing large amounts of data. Usually you can buy a CD/DVD-R/RW drive, often called a "super-drive."

A newer format is dual-layer media, which is notated as "DL."

At first, there was a "format war" between the two types. Today, most DVD drives are "±" hybrid drives which can use both types of media. However, since "plus" discs usually cost about 25% more than "minus" disks, the "minus" discs are much more popular.

"RAM" discs are part of the "minus" family, but they never became popular. You can still buy them, but they are expensive and are used very rarely.

Capacity

Regular CDs have a capacity of 650 or 700 MB.

Standard DVDs have a capacity of 4.7 GB, but special types can hold more data (dual-layer, for example, can hold 8.5 GB).

Right now, High-Definition DVDs are now coming out. We need DVDs with higher capacities because HDTV ("Hi-Vision" in Japan) videos are a lot bigger and need discs with more space. The two types of DVDs trying to capture the market were Blu-Ray and HD-DVD, but HD-DVD failed--Blu-Ray is now the winner, and will be the format everyone uses. Blu-ray discs can hold anywhere from 25 GB to 200 GB.

The capacities with an asterisk* are ones that are not for sale at this time, but are expected in the future. Just this month (July 2008) a 16-layer, 400 GB Blu-Ray disc was announced by Pioneer. There is no news on when such discs would become available, however.

Costs

Prices for popular optical media have dropped quite a lot in the past 4 years. I sampled the cheapest prices for discs four years ago, and then again this year. Here is a chart showing the different prices, and the % change over 4 years. The chart is sorted by price per MB--that is, how much you pay for each 1 MB of storage space--with cheapest at the top, and most expensive at the bottom.