This is a selective list of terms relevant to CD-R with explanations rather than definitions. Organized and authoritative information may be found (as usual) in the FAQ at http://www.cdrfaq.org/ and at Roxio's site. Much of this information is controlled by standards; many of those standards are controlled by the International Standards Organization (ISO). Those pertaining to Compact Disc are in the evolving document, ISO 9660.
NOTE: I look forward to getting information to correct any errors and will consider suggestions or requests for additional entries. I am not interested in arguments about facts, particularly if 'somone' told you ... If you read the INet long enough, someone will tell you whatever you want to hear. You will 'hear' that a CD-ROM can write CD-R, that LaserDiscs are digital, and that Saddam Hussein and Benjamin Netanyahu are lovers. I am not interested in rumor, wishful thinking or anything but traceable fact.
LaserDiscs and CD-V's are analogue, not digital. Their video and audio data are not read or written on a computer. Digital data on a LD are encoded into analogue to be recorded. Regardless, these media are not readable or writable with CD-ROM or CD-R.
DVD used to stand for Digital Video Disc or for Digital Versatile Disc. It now stands for DVD. It is a medium with great potential for entertainment and for data storage - and is important in the development of CD-R. However, DVD is in flux right now and what it will become is TBD.
The DVD players in your local electronics superstore are the video counterpart of CD players. The format used on DVD movies is MPEG 2. First, that is not the same as MP2 - MPEG 1 Level 2 - which is an audio format. MPEG 2 is implemented in hardware, not software. Creating an MPEG 2 file at this point takes a workstation, hardware and software that would buy a small house in most parts of the world. This is a job for a powerful PC and for many purposes is better handled in specialized hardware.
A single DVD can hold over 5 GB of data and a few applications see value in exploiting it. While this is not the place to go into technical depth, it is worth pointing out some important technical differences between DVD-ROM and CD-ROM. Maybe it's enough to say that DVD's may hold two or more tracks on each side and may be written on both sides of the disc.
DVD-ROM readers can read DVD movies, DVD-ROMs and pressed CD formats. The first generation cannot read CD-R of any flavor, but later generations are Multiread and will read CD-R and CD-RW. Please note (again) that additional hardware - an MPEG 2 decoder - is required to play a DVD movie on a DVD-ROM.
There is a DVD-R on the market It writes DVD movies (built on a workstation) and DVD-ROMs.. It is commercially available for about $17,000. If you're interested in buying or using one, find an expert; I can't afford even to think about it.
There are two competing formats for DVD-RAM and first production units (under $1K) are on the market now. It is logical that at most one will win out eventually, but no one knows which format - or whether it will be another mechanism altogether. As I understand the standard format, it will read DVD movies and DVD-ROMs. A 2.6-GB blank (which may be readable in DVD-ROM) costs about $20 today; a 5.2-GB blank, which is not readable in other hardware, is double-sided and costs about $40.
Logically, DVD-RW should include DVD-R - but it doesn't. It should be a variation of DVD-RAM - but it isn't. And it should have a single standard - but guess what? Fortunately, the competitive units are not yet available; if you want to learn about it at this stage, please look somewhere else. I have all I can do to keep up with commercial products.
Now we get into the real world. Some of these things have been around long enough to be pretty well understood and even to be in regular use. The first topic is formats - in particular, those used on pressed discs. Note that discs are pressed from glass masters. The masters are made from tapes. The tapes may come from CD-R's or from other sources; the pros are not limited to starting with CD-R any more than cassettes have to come from cassette masters or video tapes from VHS tape masters. Therefore, the pros can break the 'rules' we follow in CD-R.
Properly called CD-DA (Compact Disc - Digital Audio), this is the sort of thing you drop into your Discman. Information about it is defined in the Red Book - a formal standard which is explicit and (largely) followed. The Red Book (named for the color of its cover) calls for a standard format which is not subject to argument; for convenience, I use redbook as a word for that format: uncompressed Pulse-Code Modulated (PCM) data sampled 44,100 times per second in two channels of 16 bits each and ordered and interleaved in a particular manner. With reordering, that format becomes RAW or SND on a computer. Wrapping appropriate header and footer information around a RAW or SND file produces an AU or WAV file. As discussed elsewhere in this primer, software which extracts digital audio produces WAV files; authoring software writes CD-DA from WAV files. It is worth repeating here that a conventional CD player reads exactly one closed session on a CD; anything recorded after the first session is invisible to it and if that first session is not closed or is not audio, it will not be read at all.
CD-ROM (Compact Disc - Read-Only Memory) is used to describe any CD format in which data (rather than audio tracks) are written. Hybrid modes incorporate both data and audio and are discussed below. A data track is a session and consists of a Table of Contents (TOC) and data. The TOC is translated into a FAT16 file system by the CD Extensions (such as MSCDEX). The files are any flavor of computer file. More information elsewhere in this primer addresses multiple data sessions and related matters.
On a CD-Xtra disc, a CD-DA session is followed by one or more data sessions. Since the first session is audio and closed, it will play on an ordinary CD machine. The subsequent sessions read as they would on any data CD-ROM. To satisfy the standard for CD-Xtra, the audio session and first data session must be written at once and some additional folders and data must be recorded; however, for many purposes it is sufficient simply to record a closed CD-DA session, leave the disc open, then add one or more data sessions which do not import the first. Mixed Mode is similar to CD-Xtra except that the data session(s) is written first and the resulting disc plays only in a CD-ROM or special player. NOTE: The standard requires that the audio of a hybrid mode be written TAO; some software violates the standard to support emulating pressed discs.
Home recording of CD's in various formats has been practical since about 1995. The technology is evolving rapidly, various packages of hardware and of software implement different features more or less in compliance with the standards - and confusion is increasing even faster than brands and models.
Compact-Disc Recordable (CD-R) uses a blank consisting of a polycarbonate base with a layer of dye under a metallized surface covered with a lacquer. Clear and blue dyes may be used, resulting in gold or green appearance; the metal layer is gold with those dyes. A different blue dye is overlaid with aluminum, giving a silver/blue disc. When exposed to intense laser light, the dye changes opacity to the less-intense illumination used to read a disc.
Compact Disc - Rewritable uses a different mechanism for recording. The sensitive layer is a silver-colored alloy which changes state (crystalline to amorphous) when exposed to intense laser light and which changes back to some extent when exposed to different illumination. Those state changes cannot be repeated indefinitely; the specified number of cycles for successful operation is currently 1,000. Although an erasable blank is fundamentally different from the kind used to write once, a CD-RW recorder will write CD-R without penalty.
Only some players - CD audio or CD-ROM - can read erasable blanks. CD-ROMs designated Multiread should read them reliably; others may or may not. Some audio players which read write-once CD-R media will also read erasables; some will not.
Where CD-R and CD-RW were designed to make a disc which behave like a
pressed CD or CD-ROM, packet writing is designed to allow writing comparatively
small amounts of data in the way that one writes to a floppy drive. Two
different systems are used, one for erasable blanks, the other for write-once;
they are discussed in this primer under Packet Writing. However, it is
important to note the following, which apply to reading in drives other than
the writer.
1. CD-DA cannot be written in packets; a packet disc cannot be read in an audio
player.
2. A packet-written disc may be finalized to a format readable under Win95 or
Win NT, but cannot be read at all in DOS or Win3.x.
3. A write-once packet disc may be readable without finalizing in Windows 98
and an imminent Apple system.
4. An erasable packet disc requires a driver to be read. It cannot be
finalized.
E-mail me at cdrecording@mrichter.com
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