High Speed RW
Technology - Page 1
It is unambiguously acknowledged that CD-ROM technology has moved
from a proprietary Philips/Sony format during its introductory years back into
the early eighties, to a universally accepted "de facto" standard
for distribution of audio and data content. Both its original inventors continue
to play, however, a parental role when new enhancements are being made and "ex-officio"
standards are declared, aiming to "force" compatibility among the
(possibly) diverging ways new innovators might choose to follow trying to extend
the original technology.
Pushing the existing CD-R technology into new heights requires
advances in existing media type formulations, new laser diode innovations, and
faster, lighter and more accurately driven rotors. And all this is finally based
on new designs and implementations of chips able to perform advanced DSP functions,
encoding and decoding of data streams, and head positioning adjustments at a
fraction of the time their predecessors were able to achieve.
The introduction of ReWritable media (CDRW) several years ago
stipulated the dream of ReWritable disks replacing the good old floppy. But
this came at a cost. The formulation of the new media differed drastically from
that of the original plain recorded-once disks. The new media is manufactured
by using materials which alter their laser-beam resistance according to changes
of their crystalline / amorphous phase / state, while the construction of the
former is based in dye technology.
This significant "advancement" made ReWritable disks incompatible
with earlier drives. The newer readers had to be built according to certain
criteria in order to be compatible with the new media. Standards were determined
and at this exactly place the OSTA MultiRead specifications were released and
essentially "enforced" compatibility among all new CD-ROM readers.
2. CD-R versus CD-RW technology
High Speed RW Technology
- Page 2
CD-R versus CD-RW technology
Both rely on the same logical standards. The same number of bits
is placed onto the surface of a recordable or a ReWritable disk. At exactly
the same place and format that the reading head of CD-ROM would expect them
to be. Consequently, the same on-drive electronics can be used for reading both
types of disks. This seems to have been the biggest advantage enabling quick
acceptance of CD-RW technology among drive manufacturers. Both types of disks
are recorded in one of two similar ways. Either on a track-by-track basis or
in small amounts of "chunks" called packets.
Furthermore, one or more non-packet written tracks can be recorded
under a single continuous head movement constituting a single session. If the
laser is turned on once during the recording phase of all adjacent tracks of
this section the recording is called Session-at-Once (SAO). Otherwise, it is
called Track-at-Once (TAO). Disk-at-Once is a special case of SAO mode when
no further recording on a disk is possible. Both recorded-once and ReWritable
ones behave from a user's perspective identically in all these recording modes.
Due to limitations of the encoding / error correcting features
of the original CD-audio format specifications at least 2 seconds of "silence"
have to be embedded when the laser is turned on/off. Each second of added silence
is equivalent to 75 frames, so a total of 150 frames of audio or data get lost
each time a new track is added on a disk. In terms of data bytes this is 150x2048
bytes, roughly 300KB!
Packet writing overcomes this limitation and (for drives particularly
designed for this, as all the latest ones) allows recording to be continued
by wasting just 7 frames (aka, linking blocks). 15KB versus 300KB of the earlier
case, an improvement of 2000%! The vision of a data CD becoming a large floppy
has been got very close. (Not by so much though, as we will see below
In the case of non-packet written tracks, the data files contained
on a single track follow the strict rules defined by the ISO-9660 standard and
some of its proprietary extensions (such as Joliet). A lot of (disk) space is
wasted for joining adjacent tracks, resulting to inefficient disk-space use,
as noted above.
When packet writing is used, the recording head with the help
of the underlying drive-logic turns the recording of the "actual"
data on and off at a much smaller time frame. By adjusting suitably the way
the "Table of Contents" (TOC) is stored on the disk, a much better
disk-space use is being made. The drawback here is that reading might be slowed-down
and a (predefined) longer-than-necessary TOC might incur additional disk storage
waste on a disk.
There are, however, a number of important, and in some cases even
difficult to "cure", disadvantages that (current) RW technology imposes...
3. CD-R versus CD-RW technology - The "differences"
High Speed RW
Technology - Page 3
- CD-R Technology
The manufacturing of CDR disks is currently based purely on dye
technology. This being the oldest method results to sequential disk recording
at the highest possible bitrates. With over a handful dye-makers and several
dozen -licensed- disk manufacturers the media cost has become very low. Consumers,
when buying recorded-once disks, now spend almost the same amount of money once
spent for purchasing floppy disks
Moreover, being the first writable format released it has enjoyed
the widest possible acceptance. Conventional CD-ROM readers can usually read
recorded disks without problems. In some cases, we have found some of them to
be able to read more easily highest-quality recorded disks than pressed ones!
According to psychological / sociologic studies carried out by some manufacturers
in the past the only disadvantage of these disks seems to be their write-once
limitation. If used for archiving purposes and quick-and-cheep data dissemination
CDR seems to be unbeatable.
Media life expectancy is (by most projections) over 50 years.
For some dye/manufacturing combinations estimations are as optimistic as to
claim it to be over 250 years!
- CDR-W Technology
Instead, CD-RW media manufacturing is based on phase-change technology.
The following figure (courtesy of Phillips) shows the different layers and materials
used for constructing a ReWritable disk:
As it is not the case with CDR disks, media of this type can be
randomly (re) written in a fashion that reminds end-users of large floppies.
The only advantage proves to be the ability of the disks of this type to be
And we explain this by comparing RW media with those just recordable
- Life expectancy is much lower, usually no more than 30 years.
- The reading speed of most current CD-ROMs is much lower on ReWritable than
- Fixed-length packet writing usually employed on ReWritable wastes more of
the totally available disk space.
We can continue this list a little more. But we will stand at
a point requiring special attention. According what both others and us have
found from practical experience, RW technology is NOT foolproof. Useful real-life
of these is much, much less than 1000 erasing cycles. We have seen disks from
established manufacturers to be completely unreadable after just one year of
The worst nightmare of every CD user, i.e., dust and small scratches
on the lower surface of a disk seems to become much more important when it comes
to ReWritable media. Due to continuous use (and misuse some times), the lower
reflectivity and weaker laser beams used to read them, the recording quality
deteriorates much more rapidly than in the case of recordable once media. Certainly,
this is not just our personal observation. It is known that the original S/P
red-book specifications are the primary guilds for this.
Panasonic engineers (and others) acknowledged this early and
so suggested disks to be included in a case when they purposed the DVD-RAM specifications.
Regardless of how strongly many have rejected this idea, we personally think
is among the wisest to hear so far on this subject!
Another weak point concerning RW technology concerns its recent
advancements in comparison to respective advances in the CDR case. 12x speed
recording-once has almost become the standard. By the end of the year the majority
of the to-be-shipped drives will be able to record at this speed. RW technology
has only recently seen announcements for greater than 4x speeds. And worst than
this, the new media types and recording methods necessary for doing this seem
to introduce further incompatibilities.The main theme of this article will thus
necessarily shift focus on this subject below.
So ReWritable can be used mainly for temporary storage and interchange of
files where the cost of writing once a CDR disk and then throwing it away is
both a money and environmental waste.
4. The new Orange Book part III extension
RW Technology - Page 4
The new Orange
Book part III extension
Philips recently introduced a new extension to the original Orange Book specifications.
Part III, volume 2 is now part of the extended "standard". And it
concerns reading and recording of the new high-speed CD-RW media. Will this
new standard change the way we use RW recording and especially packet writing?
As you all know almost every new CD-R drive sold today supports both CD-R and
- The features of the new specifications:
We reproduce below from an original Philips leaflet (with some additions,
corrections and clarifications):
- Higher capacity: CD-RW with fixed-packet size
can offer more than 550 MB of randomly overwritable storage capacity.
- Highest possible transfer rate during recording: by increasing the max speed
to 10x, high transfer rates up to 1.5 MB/sec can be achieved
- Shortest possible access time: allowing CAV mode avoids spin-up/spin-down
time losses during medium access.
- By more than doubling the maximum write speed and including CAV read/write
capabilities, the high-speed CD-RW standard sets new milestones for removable
In the following picture (due to Philips)
a single recording signal is represented both at the inner part of a disk and
at its outer surface. It is easily seen that if CAV recording mode is allowed
the laser has to adjust the 0/1 pulses throughout the disk-recording phase.
At the outer part of the disk, where bits are to be recorded at a higher rate,
these pulses are more rapid:
The short pulses at the outer place of a disk
can be reliably applied only if the underlying medium characteristics permit
this. (Provided the laser head has also been designed by taking this into account!)
The improved chemical synthesis of all higher speed RW disks assures that this
will be now possible. For all this to be achievable new media formulations have
been defined and recording strategies are to be adopted.
So the natural question arises:
What is the backward compatibility of high-speed CD-RW?
Because of time-constraints concerning the chemical
reactions occurring during recording and the synthesis of the used materials,
CD-RW media designed for high speed rewriting (in general) can not be properly
rewritten at current 1x~4x speed drives. Subsequently, several precautions have
been adopted and implemented into the new specifications.
Media of the new type are identified by a new
subtype setting in ATIP (Absolute Time in Pregroove: this is the place onto
a disk's surface designed for helping the laser-head into following the correct
spiral path while recording---it is also used for storing critical media characteristics
to assist the drive into correctly identifying the inserted blank media and
consequently properly adjusting the laser power for recording).
Thankfully, many current drives do not recognize
this new setting. Some of them will not even attempt writing on a disk of this
type. Some (regretfully) might try doing this, though. In this case they will
choose their default speed and writing strategy. This is most of the time and
the highest possible one (4x). Data lose might result in such a case
To take care for this case, in the new media the
ATIP location (where disk information concerning speed and writing strategy
is stored) has been moved onto a (slightly) different place to ensure that older
drives will not recognize the newer disks and so they will not attempt writing
on them. (Admittedly, a quite clever solution.)
It is furthermore expected that firmware upgrades
offered by the original drive makers will force the latest 4x writers to correctly
identify new higher-speed disks. It is even possible by adapting the drive's
writing strategy in this case to enable current drives to record correctly on
disks of the new type. Such upgraded drives can write at 4x with an adapted
The following table (again due to Philips)
summarizes the abilities of old and new drives:
part III, vol 1, v1.0
part III, vol 1, v2.0
1x, 2x & 4x
part III, vol 2, v0.9
reject for writing
Current 4x drive
1x, 2x, or 4x
reject for writing
Upgraded 4x drive
1x, 2x, or 4x
writes 4x only
high-speed CLV drive
10x CAV drive
1x, 2x, or 4x
1x, 2x, or 4x
1x, 2x, or 4x
any CLV 4x
10xCAV (32 Hz)
any CLV 4x or 10xCAV
- A First Conclusion
CD-ROM has replaced the floppy as standard medium for programs distribution.
CD-R has replaced the floppy and tape streamer as standard medium for back up
and archiving of home users.
CD-RW might be the right replacement for the floppy
as a standard medium for temporary storage and data interchange. With the adoption
of high speed RW recording this will certainly vastly improve in the near future.
We should be able, in the near future, to correctly measure and test the RW
abilities of both new readers and recorders. The CDRInfo team is positioned
into bringing this to its audience in the next round of both hardware and software
tests. The improved recording speeds of new media/drive combinations following
the new standard has further commissioned us into doing this?
5. Packet writing and BURN-Proof
RW Technology - Page 5
There is also another fascinating technology
able to help the RW packet writing market to grow?As mentioned in the introductory
material of this article, packet writing shrinks the free space of a RW disk
down to just over 500MB. This happens due to packet writing standard v2.0
limitations. Most of you will certainly remember our recent overview of the
BURN-Proof technology. It not only prevents buffer underrun but can also help
RW recording. The following figure from Sanyo graphically depicts all this:
you might ask: If BURN-Proof is adopted for packet writing, the link
area will be just two (2) sectors when the original packet-writing specification
requires seven (7) seven sectors.
This means that over 600MB of free space is
available for fixed-packet writing, when the previously available formatted
size was about 530MB! If this lack of space has held some people from using
packet writing (well, it was actually some various other incompatibility problems
as well...), then this will no more be the case.
Of course there are some other problems preventing
the industry from adapting the "BURN-Proof packet writing" method.
The main problem is that the new method isn't backward compatible with the
UDF specification. Each new, enhanced, UDF reader will have to support the
new format as well. We expect (and hope) that this will be solved in the near
- When should we expect to see the new higher-speed CD-RW drives?
As you might already know Yamaha will be the first company to ship a CD-RW
drive with an 8x RW writing speed during May. Plextor and Ricoh announced 10xRW
recording drives which probably will ship in June. Other manufactures (LG, Acer)
plan to ship increased RW writing speed drives in June (12/8/32), but this might
take longer since there is currently a shortage of shipping chipsets from the
Last we know for sure that several 10xRW drives
are out for beta testing, so don't dare to think that the new high RW speed
drives are too far away ;)
- What about High Speed RW recording media?
Ricoh recently announced new High Speed RW recording media which is compatible
with the newest 10xRW recording CDR-W drives and has the special logo "High
Speed RW" printed on a surface of the disk:
You can also see below the new Logo for high speed RW recording:
New High Speed RW Recording Logo
Old RW Recording Logo
6. Info about Yamaha CDR-W drives
RW Technology - Page 6
Info about Yamaha
As you already know the first CDR-W drive
which will support 8x RW recording speed will be Yamaha 8824s since it ship
this month (May 2000). Below is some information about what will happen
with the new and the old CDR-W drives from Yamaha:
- The standard of ReWritable CD is classified in two categories
The current standard specified up to 4x writhing.
Media supported by only 2x writhing is also selling.
Orange Book Part III volume1 v2.0
The new standard added at this time.
No recorder supports 4x-10x (CAV) at present.
The special logo "High Speed RW" is printed
on a surface of the disk
Orange Book Part III volume2 v1.0
Background : According to the current standard,
RW media cannot be given proper phase-changed face by faster writhing more
- What will happen with Yamaha CDR-W drives?
The CRW8824 supports both standards above. Yamaha plans, in order to show
the capability of high speed ReWriting, to print a special logo "High Speed
RW" on a surface of the recorder. The recorder having this logo is able
to use the high speed ReWitable CD.
All old recorders cannot burn the high speed
ReWritable CD. The possibility of reading the burned high speed ReWritable
CD depends on each recorders. In case of Yamaha, old recorders may not be
able to recognize the high speed ReWritable CD and may give user's Computer
environment instability. In order to improve this situation, Yamaha plans
to give into their old models the read capability by updating firmware:
For High Speed CD-RW writing, erasing, or reading, both the drive and the disc
must bear the High Speed CD-RW logo. When using a CD-ROM drive to read this
disc, the drive must be capable of reading CD-RW discs.