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or land is too long, the drive's clock will drift too far and possibly
get out of sync.  (This is why "blank" recordable discs aren't entirely
blank: they have a pre-cut spiral groove with a "wobble" that the recorder
can use as a timing signal.  A clock accurate enough to produce a stable,
reliable signal at these frequencies is too expensive to incorporate into
a cheap consumer product.  The 22.05KHz wobble is frequency-modulated by
+/-1KHz to create the ATIP signal that, in the lead-in area, holds some
bits of information about the disc.)

To guarantee pits of specific lengths, the CD standard requires that
there are at least 2 and at most 10 zeroes between every 1.  This is
achieved by converting every 8-bit byte into a 14-bit value, a process
called Eight to Fourteen Modulation (EFM).

The shortest possible pit (or land) thus represents 3 EFM bits (100),
and the longest 11 EFM bits (10000000000).  If a single bit requires time
T to pass under the read head, then pits of these lengths can be referred
to as 3T pits and 11T pits.  If after seeking to a new location, the drive
sees a pit shorter than 3T or longer than 11T, then it immediately knows
that the disc is not spinning at the rate it was expecting, and can make
appropriate adjustments.

Between each 14-bit EFM word there are 3 "merging bits".  Because CDs aren't
allowed to have runs shorter than 3T or longer than 11T, it is sometimes
necessary to follow an EFM code with a 1 or 0.  Suppose, for example, that
an EFM code ending in 1 were immediately followed by an EFM code starting
with 1.  The merging bits also serve to prevent the frame synchronization
pattern from appearing where it isn't supposed to (see next section).

If there is more than one possible arrangement of merging bits that satisfy
the restrictions for run length and sync pattern, then a pattern is chosen
that minimizes the low-frequency components of the signal.  This is done by
minimizing the Digital Sum Value (DSV), computed by adding one to a counter
for every T after a transition to a land, and subtracting one for every
T after a transition to a pit.  Adding a 1 to the merging bits inverts
the signal by causing a transition from a pit to a land or vice-versa.
Minimizing the DSV is important because low-frequency signals can interfere
with the operation of tracking and focusing servos.

With EFM there are more bits to encode, but the highest frequency
possible in the output signal is decreased.  The ratio of the number
of bits transmitted to the number of transitions on the medium is high,
making this an efficient way to store the data while still being able to
recover the clock.  It's also worth noting that a 3T pit is 0.833um long,
while the laser spot is just over twice that length at 1.7um.  If 2T or
1T pits were allowed, the laser would have a hard time detecting them.
This is why it's important that transitions not occur too frequently:
the laser is good at computing the time between transitions, but isn't
so good at noticing transitions if they follow each other too quickly.
Making the transitions more obvious requires making the pits and lands
longer, which reduces the amount of data that will fit on the disc.
(See the description of AMQ in section (2-41).)


Subject: [2-43-3] What's a frame?  CIRC encoding?  How does ECC work?
(2004/01/14)

EFM encoding is applied to a series of bytes called a "frame".  Some
sources -- including the SCSI-3 MMC specification -- refer to a CD sector
as a "frame", but that's incorrect usage.  A frame holds 24 bytes of user
data, 1 byte of subcode data, and 8 bytes of parity (error correction),
for a total of 33 bytes.

When read from the disc, each frame is preceded by a 24-bit synchronization
pattern and 3 merging bits.  The sync data has a unique pattern not
found elsewhere on the disc, and it ensures the read head correctly
finds the start of the frame.  (The pattern is 100000000001000000000010,
three transitions separated by 11T, which can't occur otherwise because
the merging bits are specifically chosen to prevent it.)  If you don't
understand why having a sync field is important, remember that every time
the read head seeks to a new part of the disc or is confused by a scratch,
it has to start reading in the middle of a stream of 1s and 0s and try to
make sense of what it's reading.  Until it sees a synchronization pattern,
it has no idea if it's reading the start or middle of a frame, or even if
it's at the start or middle of an EFM word.

The rest of the 33-byte frame is read as 14-bit EFM values followed by 3
merging bits.  This means there are 588 (24 + 3 + (14+3)*33) "channel bits"
in a frame.  This 588-bit structure is called a "Channel Frame".

Once EFM is decoded and the merging bits discarded, we are left with an
"F3 Frame".  The subcode byte is removed, and the remaining data (now an
"F2 Frame") is passed into the CIRC (Cross-Interleave Reed-Solomon) decoder.
The decoder is an important part of the reason why CDs and CD-ROMs work.

The raw error rate from a CD is around 1 error per 100K to 1 million bits.
That's pretty good, but at 4 million bits per second (588 channel bits
per frame x 98 frames per sector x 75 sectors per second = 4.3218Mbps),
the errors add up quickly.  CIRC encoding takes the 192 bits (24 bytes)
of data and 64 bits (8 bytes) of parity, shuffles it around, and performs
some weird math involving Galois Fields.  The bits are processed by two
error correction stages, referred to as C1 and C2.  The efficacy of the
results can be expressed as a set of error counts.

Errors are noted with a two-digit number that indicates the number of
errors with the first digit and the CIRC decoder stage with the second
digit.  The E11 count indicates the number of single-symbol (correctable)
errors in the C1 decoder.  E21 indicates double-symbol (correctable)
errors in C1, and E31 indicates triple-symbol (uncorrectable at C1)
errors in C1.  The sum of these counts is the Block Error Rate (BLER),
a measure of correctable and uncorrectable errors.  The CD standard
sets the acceptable limit to 220 BLER errors per second, averaged over
a 10-second stretch.

The E12 count indicates the number of single-symbol (correctable) errors
in the C2 decoder.  Because the data is interleaved after the C1 pass, one
E31 error can generate up to 30 E12 errors, so a high error count here is
not problematic.  E22 counts double-symbol (correctable) errors, which are
a bad sign.  The sum of E21 and E22 form a burst error count (BST), which
can be used to identify physical defects on a disc.

Any E32 errors, representing triple-symbol (uncorrectable) errors in the C2
decoder, result in damaged data.  For an audio CD interpolation is performed,
for a CD-ROM the damaged data must be repaired at a higher level.  (This,
incidentally, explains how some forms of audio CD copy protection work.
The CD author introduces deliberate uncorrectable errors to the CD.
An audio player will inaudibly interpolate across them, but a CD-ROM
performing digital audio extraction will simply return the bad bits.)

With CIRC, the bit error rate is reduced to one in 10 to 100 billion.  The 24
bytes that comes out of the CIRC decoder are referred to as an "F1 Frame".

It's worth noting that the subcode channels are not CIRC-encoded, and hence
are the least-reliable storage directly accessible to the user.  The EFM
encoding provides some protection against single-bit errors, because only
256 of the 16,384 possible combinations are valid, but without any parity
bits the best the drive can do is tell you that it failed to read the
data correctly.  The Q subcode channel, which can hold vital information
about the disc, has a 16-bit CRC.


Subject: [2-43-4] What's in a sector?
(2002/12/11)

98 frames of 24 bytes are combined to form a 2352-byte sector and 98
bytes of subcode data.  The sector is assembled from F1 Frames, which are
byte-swapped, shuffled, and run through a descrambler.  The purpose of
the scrambler is to reduce the likelihood that regular bit patterns will
induce a large digital sum value.

It should be pointed out that the 2352-byte sector is the smallest unit
most CD-ROM drives will allow software to manipulate.  It's only after all
of the above that low-level CD-ROM operations, like "RAW DAO-96" reads and
writes, begin.  This is why making a "bit-for-bit" copy of a disc is tricky.

A sector on an audio CD holds 2352 bytes of data.  16-bit stereo samples
require 4 bytes per sample, so there's 2352/4 = 588 samples per sector.
At 75 sectors per second, that's 44100 samples per second (44.1KHz).
At this point, the processing for an audio CD is essentially complete.
CD players feed the samples through a DAC (or S/PDIF connector) and
eventually out to the speakers, and send the subcode data to the front
panel controller so it can update the HH:MM counter and track number.

A sector on a CD-ROM holds 2048 bytes of user data, leaving 304 bytes for
other purposes.  Every data sector begins with a 16-byte header:

 - 12-byte sync field (00 ff ff ff ff ff ff ff ff ff ff 00)
 - 3 byte address (minute, second, fraction (1/75th) of a second)
 - 1 byte mode

The sync field and address are important because early CD-ROM drives
weren't able to accurately determine the start of a sector.  The drives
were based on CD players, which just shoved the decoded frames into one
FIFO and the subcode data into another.  The CD-ROM firmware was presented
with a stream of bytes, and expected to make sense of it.  This situation
is also responsible for audio extraction "jitter", discussed at length in
section (2-15).

The mode byte determines what the remaining 2336 bytes in the sector
looks like:

 - Mode 0: null data; serves no practical purpose for CD recording
 - Mode 1: the typical CD-ROM layout
   - 2048 bytes of user data
   - 4 bytes of EDC (Error Detection Code, a 32-bit CRC)
   - 8 bytes of reserved space, set to zeros
   - 172 bytes of "P" parity
   - 104 bytes of "Q" parity
 - Mode 2: 2336 bytes of user data, usually used for CD-ROM/XA (see below)

The Mode 1 CD-ROM ECC is independent of and in addition to the CIRC encoding.
It uses a Reed-Solomon Product Code (RSPC) to achieve a combined error
rate of 1 error per 1e15 (quadrillion) bits.

CD-ROM/XA (eXtended Architecture) Mode 2 extends the definition of a Mode
2 CD-ROM.  Form 1 looks like a slight rearrangement of a Mode 1 sector,
with the 8 bytes of space moved ahead of the user data and filled with
a sub-header.  Form 2, intended for compressed audio/video data, has the
8-byte sub-header, 2324 bytes of data, and an optional 4-byte EDC code.
The sub-header contains some channel and data type flags.

A CD session must be written in a single mode, but the XA spec allows the
form to change.  Using CD-ROM/XA Mode 2 allows you to choose between extended
error correction and increased data capacity, and also change your mind
several times in a single track.


Subject: [2-43-5] What's in a subcode channel?
(2002/12/11)

There are 8 subcode channels, labeled P,Q,R,S,T,U,V,W, or sometimes "P-W"
for short.  (The ECMA-130 standard refers to subcode bytes as "Control
bytes".)  Every frame contains one byte of subcode data, and each byte holds
1 bit of P, 1 of Q, and so on.  The bytes from 98 consecutive frames are
combined to form a subcode "section".  The first two bits in each channel
are used for synchronization, leaving 96 bits of useful data per channel
(which is where RAW DAO-96 gets its name).

The P and Q channels are defined by the CD audio standard.  (They are
unrelated to the P and Q parity fields.)  The P channel can be used to
find the start of a track, but in practice most devices use the more
sophisticated Q channel.  Q contains four chunks of information: control
(4 bits), address (4 bits), Q data (72 bits), and an EDC (16-bit CRC).

The control bits determine whether the track holds audio or data, the number
of audio channels (stereo or quadraphonic), and specifies the Digital Copy
Permitted and Pre-emphasis flags.  The address bits determine the format
of the Q data section.  Address mode 1 holds information about tracks,
mode 2 holds a catalog number (such as a UPC code, constant for an entire
disc), and mode 3 contains the ISRC (International Standard Recording Code,
constant for a given track but may change with each track).

A disc has three main regions: the lead-in area, the program area, and the
lead-out area.  Subcode Q mode 1 data in the lead-in is used to hold the
table of contents (TOC) for the disc.  The TOC is repeated continuously in
the lead-in area in case of damage (remember, no CIRC encoding on subcode
channels).  In the program and lead-out area, mode 1 contains track numbers,
index numbers, time within the current track, and absolute time.  Index 0
marks the start of a pregap (pause) before the audio in a track begins,
index 1 marks the start of the music, and indexes 2 through 99 are usually
not set but can be added if desired.

The ability to specify track and index markers when writing a Red Book
audio CD is often referred to as "PQ editing" because that information is
contained in the P and Q subcodes.

Subcode channels R through W are not defined by the CD standard, except
to say that they should be set entirely to zero if not used.  They're
currently used for CD+G (e.g. Karaoke) discs, CD-Text, and some forms of
copy protection.

It is interesting to note that, while bytes from 98 consecutive frames are
used to create a subcode "section", those frames don't have to be from a
single sector.  It's possible for a subcode section to start in one sector
and end in the next.


Subject: [2-43-6] I want even more details
(2004/02/17)

Sheesh.

An excellent reference for is Ken Pohlmann's mammoth _Principles of Digital
Audio, 4th edition_ (ISBN 0-07-134819-0), especially chapter 9 (on compact
discs) and chapter 5 (on error correction).  If you want something a little
slimmer, try his older _The Compact Disc Handbook, 2nd edition_, 1992
(ISBN 0-89579-300-8).

Another good book is _The Art of Digital Audio_, 2nd edition, by John
Watkinson, Focal Press, 1994 (ISBN 0-240-51320-7).

http://www.ee.washington.edu/conselec/CE/kuhn/cdmulti/cdhome.htm has a
number of interesting pages.  In particular, there's a good page about CIRC
on http://www.ee.washington.edu/conselec/CE/kuhn/cdmulti/95x7/iec908.htm,
and http://www.ee.washington.edu/conselec/CE/kuhn/cdaudio/95x6.htm has a
nice explanation of disc construction and optics, especially the three-beam
autofocus.

The page at http://www.tc.umn.edu/~erick205/Papers/paper.html provides
some background information on sampling, aliasing, dither, DACs, and other
relevant topics.

You can get a copy of ECMA-130 from http://www.ecma-international.org/.
This document describes the format of a CD-ROM, including physical dimensions
and optical characteristics, as well as sector formats and Q-channel specs.
It also features some interesting annexes:

 - Annex A: Error correction encoding by RSPC
 - Annex B: Scramble (a description of the pre-EFM scrambler)
 - Annex C: Error correction encoding by CIRC
 - Annex D: 8-bit to 14-Channel bit conversion (has the full table)
 - Annex E: Merging bits (algorithm for computation)

Standards documents, as a rule, are terse and difficult to understand.
ECMA-130 is actually quite readable, and if you understood the preceding
sections you should have no trouble sorting it out.

If you want source code for the CIRC, RSPC, EDC, and scramble functions,
look for Heiko Eissfeldt's edc_ecc.c (and related files).  The code is
part of Mode2CDMaker, CDRDAO, and possibly others.

If you want an explanation of DSV and the problems associated with it,
read the Philips patent on the sector scrambler (US4603413), or one of
the associated patents on removal of DC content from a digital signal.
The full text of the patent can be found at http://www.uspto.gov/.  In brief:

  "[...] If the frequency of such oscillation is comparatively high,
  during the read operation the decision level for detection of the
  channel bit signals may be rendered inaccurate. As a result, read-out
  of the information will be disturbed to such an extent that even the
  error-correction measures cannot prevent errors. Moreover, the tracking
  system for controlling the read laser which reads the channel bits may
  become incapable of keeping the laser beam accurately positioned on
  the track."

It appears that, when the DC offset in the signal becomes too large, the read
head has trouble "seeing" the disc.  The voltage level in the photodetector
has pegged, so the difference between a pit and a land is unnoticeable.

An article at http://www.digit-life.com/articles2/magia-chisel/index.html
examines why one specific file failed to record properly.  It turns out
that, after passing through the scrambler, a piece of the file has a
section that matches the sector header sync pattern.

For some technical information on how CD-Rs are constructed, look through
the uspto.gov site for relevant patents.  For example, US5348841 describes
"Organic dye-in-polymer (DIP) medium for write-once-read-many (WORM)
optical discs".


Subject: [2-44] Digital is better than analog, right?
(2002/12/30)

Not always.

Digital audio CDs are superior to audio cassettes and 8-track tapes, and
digital video DVDs are superior VHS videotapes.  However, the analog film
shown in a movie theater is superior to DVD, and the analog studio master
tape is better than an audio CD.  The sounds that an Apple II makes are
generated digitally, but you wouldn't want to play your CDs that way.

Some formats are better than others.  The low-cost consumer digital formats
are generally superior to low-cost consumer analog formats (except perhaps
for 35mm film, though that's changing).  This does not mean that "digital"
is better than "analog", though many people have that impression because
the consumer electronics companies are marketing products that way.


Digital has some advantages over analog.  The most significant is the
ability to apply various algorithms to reproduce the original digital signal.
With most forms of analog transmission, reconstructing the original signal
without noise and distortions is difficult.  The flip side is that, with too
much interference, the digital signal becomes unusable.  NTSC televisions
(the kind used in North America and Japan) can display a transmission with
a negative S/N ratio, i.e. there's more noise than signal.  (If you're not
part of the "cable TV" generation, think about a picture that was heavily
snowed, but still decipherable.  It was probably a sporting event.)

Digital also has disadvantages, although many of them can be minimized
through careful system design.  The most fundamental problem is the need
to convert the digital signal back to analog.  Human senses are analog,
so audio has to be converted to voltages that drive speakers, and video
needs to be turned into pixels on a screen.  The human eye is pretty easy
to fool -- update the image quickly enough and the brain will believe the
motion is smooth -- but the ear is more discerning.  Slight changes in
frequency and timing, especially in a stereo signal, can be detected.

Many digital formats are compressed with "lossy" techniques.  Algorithms
like MPEG-2, MP3, DTS, and SDDS remove parts of the music to reduce the
storage size.  The parts removed are usually inaudible, though that depends
on how much is removed and how good your ears are.

The upshot of all this is that it's wise to pay attention to what you're
getting.  Don't assume that a digital format is better just because it's
digital.


Subject: [2-44-1] What is "digital" and "digitization", anyway?
(2003/01/05)

Computers store things in "bits", which can be either 0 or 1.  To store
something in a computer, it must be converted to a series of bits.  The
process is called "digitizing".

You've probably seen an egg slicer.  If you haven't, picture a device
that looks like a book resting flat on table.  Instead of pages it has
an egg-shaped depression, and instead of a front cover it has a frame
with thin wires stretched across it vertically at regular intervals.
You raise the lid, insert the egg, and when you press the lid down the
wires cut the egg into thin, round slices.

It usually helps to hard-boil the egg first.

Suppose we want to digitize an egg so we can make a nifty 3D model and
display it on a computer.   Our slicer has 9 wires, so we could end up
with as many as 10 pieces.  We place the egg into the device and slice it.
Now we measure the height of each piece in centimeters (assume the pieces
are perfectly round), measuring the diameter with calipers and rounding
it to the nearest centimeter.  Each slice could go from 0cm (the egg was
short, so there was no slice) to 5cm (the width of our slicer).

When we're done, we spit out something that looks like this:

 1. 1cm
 2. 2cm
 3. 2cm
 4. 2cm
 5. 3cm
 6. 3cm
 7. 3cm
 8. 2cm
 9. 2cm
 10. 1cm

Your eggs may vary.  Storing a number from 0 to 5 requires 3 digital bits,
so if we know that measurements are always in centimeters, we can store
the height of each slice in 3 bits.  We have ten numbers to store, so we
can hold our egg in a mere 30 bits!

When we try to display our digitized egg on a computer screen, however, we
discover a problem.  The image doesn't look like a smooth egg.  Instead,
it looks like a bunch of stair steps in a vaguely egg-shaped pattern.
The sizes aren't right either: our original egg was actually 3.4cm at its
widest point, but we had to round it down to 3cm.

Suppose we improve our measurements down to the nearest millimeter.  Now,
when we have to round off the measurements, the round-off error is much
smaller.  The results look much better, but holding a value from 0 to
50 requires 6 digital bits instead of 3, so we've doubled our storage
requirements to 60 bits.  What's more, the image still looks stair-steppy.

The stairs happen because each slice has a single height value.  When we go
from slice #7 to slice #8, we abruptly jump from 3cm to 2cm.  The reason our
recreated egg doesn't look smooth is because we didn't really capture the
original, in which each slice varied in height from one edge to the other.
Our digitization could only capture the average height of each slice.

There are a couple of ways to improve this.  The first is to guess at
the shape of the original egg, and draw smooth curves based on the data
we have.  This is called "interpolation".  The other approach is to buy a
new egg slicer with wires that are closer together, so we have more slices,
reducing the size of the jump from one slice to the next.  This is called
"increasing the sampling rate".  If you double the number of slices,
you double the number of bits required to hold the digital version.

If you slice the egg finely and measure it accurately, you can get a
nearly perfect representation of the original.  For example, if we create
slices that are one molecule apart, and measure the height to the nearest
molecule, we will have an extremely accurate picture, not to mention a
seriously huge digital representation.  The tricky part about digitizing
something is to choose the height and thickness of the slices such that
the likeness is very good but the digital size is small.


Subject: [2-44-2] How does this relate to CD-DA?
(2003/01/05)

An audio CD cuts a one-second "egg" of sound into 44100 slices, and
measures the "height" of each slice from 0 to 65535 (16 bits).  It does
this independently for the left and right stereo channels, using a format
called Pulse-Code Modulation, or PCM.  The technical shorthand, which you
may have seen in a sound editor, is "44.1KHz 16-bit stereo PCM".

Measuring the "height" of each slice is called quantizing.  The round-off
error in the measurements is called quantization error.  The problems
associated with the error can be reduced by applying "dither" (low-level
noise).

The reason for the number 44100 is explained in section (2-35).  The choice
of 16 bits is also fairly arbitrary, but extremely convenient on a computer.

There are other problems when digitizing (e.g. aliasing) and when converting
back to analog form (e.g. jitter).  See
http://www.tc.umn.edu/~erick205/Papers/paper.html for an introduction.

Newer audio formats, such as Super Audio CD and DVD-Audio, offer different
sampling rates (up to 96000), quantization (up to 24 bits), and numbers of
channels (e.g. 5.1 surround-sound).


Subject: [2-45] What's a CDR-ROM?  CD-PROM?
(2003/02/28)

The term "CDR-ROM" was coined by Optical Disc Corporation in a February
2003 press release, and refers to a disc with writable and non-writable
components.  Some possible uses include burning a unique serial number on a
full CD-ROM, or providing recordable discs with marketing content (e.g. a
few tracks of audio to which more music can be added).  More information
can be found at http://www.optical-disc.com/.

Eastman Kodak had a similar product, called the "CD-PROM", a few
years earlier.  According to their web site, marketing and sales
of the CD-PROM was discontinued in October 2002.  See the notice on
http://www.kodak.com/US/en/digital/progCDR/.


Subject: [2-46] What's HD-BURN?  GigaRec?
(2003/05/02)

In April 2003, a few companies began announcing technologies that allow you
to store larger quantities of data on standard CD-R media.  Unlike DD-R
and "ML" technology, special discs aren't required.  The capacity and
compatibility is different for each.

  GigaRec (Plextor)
    Increases storage capacity by 40%, allowing up to 1GB on a 700MB disc.
    The discs can be read on some unmodified CD-ROM drives.
    http://www.plextor.com/english/news/press/pr04142003.html
  HD-BURN (Sanyo)
    Doubles disc capacity of an 80-minute disc from 700MB to 1.4GB.  A
    firmware change is required before a drive can read the discs.
    Support for extended-length CD-RW media is planned.
    http://www.digital-sanyo.com/BURN-Proof/HD-BURN/

Does it make sense to use these?  The extra capacity is handy, but data
is only useful if you're able to read it.  Check the compatibility of the
hardware you're going to use to read the discs.


Subject: [2-47] What are C2 errors?  What do they say about disc quality?
(2004/04/15)

When people talk about "C2 errors" they are usually referring to the rate
of uncorrectable errors found on a CD.  For an overview of error correction,
see section (2-17).  For a more detailed look, see section (2-43-3).  These
values are returned by "surface scan" tools.

There are two flavors of C2 errors, and not all drives are capable of
reporting both.  Uncorrectable C2 errors indicate data that has been lost.
On an audio CD the missing sound samples will be smoothed over, and on
a CD-ROM the errors may be corrected by an additional level of error
correction, so the flaws may not be noticeable.  Correctable C2 errors
indicate data that is whole but will be lost if the disc degrades any futher.

The fewer errors of either kind, the better.  The results you get are the
combination of the writer and the media, and in some cases may be influenced
by the quality of the device used to read the CD.  If performing the same
set of operations on two different brands of discs results in consistently
lower error rates on one brand than the other, you will probably be better
off with the lower-error-rate brand.  It is entirely possible that a
different writer would yield the opposite results, so it's not reasonable
to say that brand X is better than brand Y without performing a rigorous
test with a variety of different recorders.

Some discs are poorly constructed, and may deteriorate faster than others.
For long-term archiving, it may be useful to re-examine discs periodically,
especially if you buy "cheap" discs in bulk.  Having fewer errors today
means little if the disc is unreadable in six weeks.

For drives capable of reporting the errors, you can use Nero CD Speed
(http://www.cdspeed2000.com/) to evaluate the error rate.  For a more
thorough examination, you can buy "CD Inspector", which comes with software
and a slightly modified CD-ROM drive
(http://www.hda.de/english/products/checker/cd-inspector/cd-inspector.html).


Subject: [2-48] What are CD+R and CD+RW?
(2003/11/17)

Simply put, they aren't.

There is no such thing as CD+R or CD+RW.  There are a number of different DVD
formats, including DVD+R and DVD+RW, but so far CDs only have -R and -RW.
CD formats with a '+' in them (except for CD+G, which only defines the
subcode channels of an audio CD) are usually typographical errors.


Subject: [2-49] What's HighMAT?
(2003/12/02)

HighMAT stands for High Performance Media Access Technology.  Co-developed
and supported by Microsoft and Matsushita (Panasonic), it was first announced
in October 2002.  HighMAT defines formats for storing digital media (music,
photos, videos) on CD-R/RW discs and writable DVD formats.

While many DVD players now recognize MP3 and JPG files on ISO-9660 discs,
they don't all do things the same way, and may not support all formats.
A HighMAT-compliant player would be able to handle all files on discs
created in HighMAT format.  The end result is that you would be able to
send a disc full of music or pictures to anybody with a HighMAT player
and know that it will work.

This format has not yet been adopted by most consumer electronics companies,
so it remains to be seen whether this will become a significant feature.

For details, see http://www.highmat.com/.


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