Currently we have four different types of CD-Rs:

•  80 Min CD-R, 700 MB capacity

•  90 Min CD-R, 800 MB capacity

•  24 Min Mini CD-R, 210 MB capacity

•  6 Min Visiting Card CD-R, 49 MB capacity

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CD-Rs employ a polycarbonate substrate, a reflective layer, and a protective top layer. Sandwiched between the substrate and reflective layer, however, is a recording layer composed of an organic dye. A pre-grooved spiral track is used to guide the recording laser along the spiral track. This greatly simplifies the design of the recorded hardware and ensures disc compatibility. A laser in the CD recorder creates a series of holes in the disc's dye layer called 'pits'. The spaces between the pits are called 'lands'. The pattern of pits and lands on the disc encodes the information and allows it to be retrieved on an audio or computer CD player.

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A session is a recorded segment that may contain one or more tracks of any type. The CD recorder doesn't have to write the entire session at once, but the last session on a disc must be "closed" before a standard audio CD or CD-ROM player will recognize it. Additional sessions can be added until the "disc" is closed or there's no space left.

Multisession writing was first used on Photo CD discs, to allow additional pictures to be appended. Today it's most often used with "linked" multisession discs, and occasionally for CD-Extra discs. These require a bit more explanation. When you put a data CD into your CD-ROM drive, the OS finds the last session on the disc and reads the directory from it. (Well, that's how it's supposed to work. Depending on your operating system and CD-ROM drive, you may get different results.) If the CD is ISO-9660 format - which it almost certainly is unless it's a Macintosh CD written in HFS - the directory entries can point at any file on the CD, no matter which session it was written in.

Most of the popular CD creation programs allow you to "link" one or more earlier sessions to the session currently being burned. This allows the files from the previous sessions to appear in the last session without taking up any additional space on the CD (except for the directory entry). You can also "remove" or "replace" files, by putting the new version into the last session, and not including a link to the older version.

In contrast, when you put an audio CD into a typical CD player, it only looks at the first session. For this reason, multisession writes don't work for audio CDs.

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There are eight subcode channels (P, Q, R, S, T, U, V, W). The exact method of encoding is beyond the scope of this FAQ, but it should be noted that the data is distributed uniformly across the entire CD, and each channel can hold a total of about 4MB.

The P subcode channel can be controlled with the JVC/Pinnacle recorders, but apparently isn't used for much.

The Q subcode channel includes useful information, which can be read and written on many recorders. The user data area contains three types of subcode-Q data: position information, media catalog number, and ISRC code. Other forms are found in the lead-in, and are used to enable multisession and describe the TOC (table of contents).

The position information is used by audio CD players to display the current time, and has track/index information. This can be controlled when doing Disc-At-Once recording.

The ISRC (International Standard Recording Code) is used by the recording industry. It states the country of origin, owner, year of issue, and serial number of tracks, and may be different for each track. It's optional; many CDs don't use this. The media catalog number is similar, but is constant per disc. Note these are different from the UPC codes.

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It depends on how much data you're going to burn, and how fast your drive is. Burning 700 MB of data takes about 80 minutes at 1x, 40 minutes at 2x, and 20 minutes at 4x, but you have to add a minute or two for "finalizing" the disc. Remember that single speed is 150KB/sec, double speed is 300KB/sec, and so on.

If you have half the data, it will finish in (about) half the time.

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There are two basic ways of writing to a CD-R. Disc-at-once writes the entire CD in one pass, possibly writing multiple tracks. The entire burn must complete without interruption, and no further information may be added.

Track-at-once allows the writes to be done in multiple passes. There is a minimum track length of 300 blocks (600K for typical data CDs), and a maximum of 99 tracks per disc, as well as a slight additional overhead associated with stopping and restarting the laser. The disadvantage of track-at-once is that most audio CD players will play the run-in and run-out blocks between tracks, resulting in slight but annoying clicks between tracks.

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CDs don't have circular tracks. They're laid out on a spiral, with multiple sessions composed of multiple tracks composed of sectors, and the data in the sectors is interleaved. The sector format is standard, but there's more than one standard. ("The nice thing about standards is that there's so many to choose from" - Andrew S Tannenbaum)

The ability to read certain portions of a CD depends on the CD firmware. Some CD players aren't capable of understanding multi-session discs or reading digital audio tracks as if they were data.

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Amkette CD-Rs come with a protective Durashield coating. The shelf life of an unrecorded Amkette disc is estimated at between 5 and 10 years. Once the disc has been written it can last upto 75 - 100 years.

Exposing the disc to excessive heat, humidity, or to direct sunlight will greatly reduce the lifetime. Thus, leaving a CD-R in a hot car isn’t good for the disc and will probably shorten its effective life.

In general, CD-Rs are far less tolerant of environmental conditions than pressed CDs, and should be treated with greater care.

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Only if you're careful. Some adhesives can dissolve the protective lacquer coating if the adhesive is based on a solvent that the lacquer is susceptible to. Asymmetric labels can throw the disc out of balance, causing read problems, and labels not designed for CDs might bubble or peel off when subjected to long periods of heat inside a CD drive. It is safe to use Amkette CD Labels which have been specially manufactured for CD/DVD labeling purpose.

When writing titles and other information on the label, these should be written in the printed area using an oil-based felt-tipped pen. Most important part is to use a felt tip pen and not a ball-point, because the top layer is somewhat delicate.

Specific information can sometimes be found on the back of the jewel case that the disc comes in.

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