High Speed Re-Writing Format - Printer Friendly version

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

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"

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!

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 directly overwritten.

And we explain this by comparing RW media with those just recordable once:
- 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 recordable.
- 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 archiving!

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

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 CD-RW formats.

- 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 storage media.

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 write strategy.

The following table (again due to Philips) summarizes the abilities of old and new drives:

Media Drive	*part III, vol 1, v1.0* 2x-only	*part III, vol 1, v2.0* 1x, 2x & 4x	*part III, vol 2, v0.9* 4x~10x
2x drive	2x	2x	reject for writing
Current 4x drive	2x	1x, 2x, or 4x	reject for writing
Upgraded 4x drive	2x	1x, 2x, or 4x	writes 4x only
high-speed CLV drive 10x CAV drive all-speed-modes drive	2x 2x 2x	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

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:

How, 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 future.

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 original manufactures.

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 ;)

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:

6. Info about Yamaha CDR-W drives

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:

Supported Speed

Summery

Discrimination

Orange Book

2x, 4x

The current standard specified up to 4x writhing. Media supported by only 2x writhing is also selling.

---

Orange Book Part III volume1 v2.0

4x, 8x

4x-10x (CAV)

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 than 4x.

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:

Recorder Model	Firmware Update	Schedule
8424	Yes	May
6416	Yes	May
4416	Yes	May
2216	Yes	May
4260	Yes	August
2260	Yes	August
4001	No	-

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.

New High Speed RW Recording Logo	Old RW Recording Logo

1. Introduction

2. CD-R versus CD-RW technology

3. CD-R versus CD-RW technology - The "differences"

4. The new Orange Book part III extension

5. Packet writing and BURN-Proof

6. Info about Yamaha CDR-W drives