MB looks appealing. NASA is among
those burning its own CD-ROMs to manage the vast quantities of images and data from its many missions.
A major advantage of CD-ROM, especially in distribution or archival applications, is freedom from errors. NASA's Planetary Data System has shipped 100,000 CD-ROMs without having a single substantiated read error. CD-R discs have similar characteristics, and at $7 per disc, they are the archivist's dream come true. The attributes of low cost, random access, and long life (100 years) make it the perfect archival medium (see the sidebar
"CD-R Solves NASA's Space Race"
).
It's the Pits
Audio CD (defined by the Red Book and developed by Philips and Sony) uses a stream of 2352-byte blocks to store digitally sampled sound. A cross-interleaved Reed-Solomon code (CIRC) provides for error detection and correction by--among other activities--spreading data over several physical sectors. CD-ROM (defined by the Yellow Book) adds 280 bytes of layered error correctio
n to each of the above blocks. This error correction kicks in if any errors get by the first layer.
Manufacturing plants produce audio CD and CD-ROM discs under clean-room conditions, for about $1000 per master and $1 per replica. The first step is to etch user data onto a master disc. Pits (indentations) distinguish data from lands (flat areas). When a laser hits a land, the laser reflects; when the laser hits a pit, the laser light scatters. Like a record album (remember them?), the tracks on a CD-ROM go in a spiral.
The next step sees the replication of the master disc on stamping masters. The stamper for CD-ROM is a plate with hills where the pits will be. Then the stamping masters create replicas by injection molding using polycarbonate resin. Finally, each polycarbonate disc gets an aluminum reflective layer and a coat of lacquer.
The advantage of this process is that you can mass-produce many copies of a master disc inexpensively (per disc). However, you realize that low cost only
when producing hundreds or thousands of discs. What if you want only a single disc, of your hard drive or whatever? Clearly, what you want is a one-step--cheaper--version of what the manufacturing plants do.
The problem is that you do not want the inconvenience of an injection-molding facility on your desktop just to produce pits and lands. That's why CD-ROM recorders simulate pits and lands optically instead of physically. CD-R (defined by the Orange Book) is essentially a CD-ROM with layers of gold overlaid with dye replacing the aluminum reflective layer. The dye is translucent, allowing the gold to reflect laser light (like a land). Burning tiny spots in the dye layer reduces the reflectivity at that spot, simulating a pit. The stamper for CD-R has a long spiral ridge that forms a pregroove in the molded CD-R disc. The pregroove wobbles to allow tracking during the recording process.
CD-R discs come in two lengths, 63 minutes (540 MB) and 74 minutes (650 MB). Because there is almost no price
difference between the two capacities, it is likely that 63-minute discs will eventually disappear.
CD-R ABCs
The figure
"CD-ROM Premastering Process"
shows the steps to produce a CD-R disc. This is a deliberate activity, as opposed to the typical ad hoc file storage on a hard disk or other medium. You generally try to fill a disc completely, because it is unlikely that you will use it again. The capability to add sessions to an already-used CD-R disc exists (it's called multisession), but the intersession gaps are so large that this procedure is undesirable. CD readers do not widely support the multisession effort. There are also some problems finding driver support to view the multiple sessions on a disc, although new hardware and drivers will recognize multiple logical volumes.
When you are designing your CD's layout, you'll have to consider the performance attributes of CD technology. CD readers have poor random-access performance (10 to 20 times slow
er than hard disks) and slower transfer rates (several times slower than hard disks). These characteristics may require redesigning a retrieval application, for example, for use on CD-R.
After designing the volume, you usually must stage the data files to local storage devices. A good network infrastructure--one with lots of space on your server--will simplify this process. An external hard drive is the second-best alternative for transferring large quantities of data between machines. The use of ZIP drives, Bernoulli or Syquest cartridges, quarter-inch cartridges (QICs), digital audiotape (DAT), or Exabyte tape introduces additional complications.
The next step is premastering. It includes selecting a volume structure for the disc, selecting the directories and files to include (generally a point-and-click operation with modern premastering software), and specifying certain attributes for files (hidden files, use of ISO-9660-compliant filenames, and the positioning files on the output volume).
After specifying this information, the premastering software will scan the source directories and report any inconsistencies. These inconsistencies usually relate to file naming or missing or damaged files.
The premastering software then reads the data files and writes an image file, which is essentially a copy of the entire CD volume. Some packages let you use the image file as a simulated CD for testing. Although this option may seem attractive, it is becoming less useful as the price of CD-R continues to fall.
The final step in the production process is cutting the disc. This step places the greatest demand on the host computer. The recording system must sustain the transfer rate (150 KBps for 1X, 300 KBps for 2X, 600 KBps for 4X, or 900 KBps for 6X) for the entire recording session. This requirement arises because the CIRC error correction spreads adjacent data across blocks recorded on the CD, so there is no way to pause and resume a session. Thermal recalibration in older hard disk models
has been the source of many CD-R recording failures. Unfortunately, SCSI device contention can also slow the throughput below the minimum. Most premastering packages can test the throughput rate and warn of problems or automatically cycle to a lower recording rate if necessary.
The post-final step is testing the resulting CD-R. You must have a test plan in place to verify CD-R contents routinely. Test methods include a checksum scheme on the data files, performing a byte-by-byte comparison of the source data to the CD-R, or using a commercially available testing program.
Several test devices will perform detailed evaluations of the physical parameters of a CD-R or CD-ROM. These include the CD-CATs SA-3 (Audio Development), the CD-Analyzer (CD Associates), and the Clover Systems tester. These devices are expensive ($5000 to $120,000) and require complicated calibration procedures to work effectively. NASA's Planetary Data System has had only moderate success in using these devices to evaluate CD-
R quality.
CD-ROM Recording Studio
That's the process. Now to get your equipment. The first critical decision in setting up a CD recording system is determining the host computer. If you need special disc types (e.g., hybrid Mac or Unix-compatible Rock Ridge discs), you'll want a recording system for that platform. Otherwise, premastering software on any platform will produce fully compatible ISO-9660 discs.
The second issue is how portable you want your recording setup to be. Will you do all your recording on a dedicated machine, or will you move the recorder to different machines? In the latter case, a combined unit like the
JVC Personal RomMaker
(which includes a power supply, hard drive, and recorder) will work best. (The Data Distribution Lab at the Jet Propulsion Laboratory uses five or six Macs for developing multimedia presentations, and the single JVC Personal RomMaker moves between systems as needed.) Unfortunately, this portability does not work
across OSes.
If your choice is to dedicate a machine to the task, that machine will need at least a 25-MHz 486 CPU, 8 MB (or more) of RAM, and a dedicated (or limited-use) SCSI connection. It should have at least two hard drives. One drive will need to be at least 1 GB, and the other at least 650 MB. The first drive (collection disk) will contain the system software, applications, and 650 MB of free space for collecting data files. The second drive will store the CD-R image file before recording the image file on the CD-R disc.
The first drive may not be necessary if other peripherals (e.g., ZIP drives, DAT drives, or network devices) will hold all the input files. Most premastering software will let you select files from any input device, but the premastering process itself is then subject to many more uncertainties. Similarly, you can forgo the second drive if the premastering software can write to the CD recorder directly without producing an image file. Again, this architecture introduces m
any more pitfalls and requires high-performance hardware on the host.
Be aware that the host computer's performance may limit your selection of a recorder. A slower machine may support a 1X or 2X recorder, but nothing faster.
The volume of discs to produce is also an issue. If producing individual discs is the norm, the recording rate is not an issue, because the setup and premastering overhead will consume most of the time for producing each disc. However, if you will routinely need multiple copies of each volume, a 4X or 6X recorder will pay for itself in a short time. In short, it is usually worth it to get a fast system to premaster your discs.
Dozens of recorders are on the market. At the low end, 1X or 2X consumer recorders from Pinnacle Micro and Hewlett-Packard sell for street prices of less than $1000. In the middle are Sony and Philips, with 2X recorders at around $2000. At the high end are Yamaha, Pioneer, and Eastman Kodak, with 4X and 6X recorders starting at $4000. For autom
ated recording, Eastman Kodak sells a Disc Transporter that automatically loads up to 75 discs. Pioneer and NSM jukeboxes support internal recorders, but at a substantial cost ($20,000 to $40,000).
Premastering programs are available from a number of vendors. Meridian Data, Corel, Incat Systems, and Pinnacle Micro provide software for PCs. JVC Information Products and Optical Media International provide software for Macs and PCs. Young Minds, Creative Digital Research, Smart Storage, and Soliton Computing provide software for Unix workstations and PCs. Elektroson's GEAR is available on many platforms and claims to support all recorders and formats. Most recorders sold today bundle adequate premastering software, or you can buy the software separately for several hundred dollars.
CD-ROM Professional
magazine is a good resource for determining the capabilities of packages.
New Discs, Old Readers?
The next logical extension to CD-R is CD Erasable (CD-E). It will use a pha
se-change technology for overwriting. Whereas CD-R mainly targets file exchange and archiving, CD-E will compete head-on with hard disk and magneto-optical (MO) systems. Furthermore, CD-E drives will support existing CD-ROMs, read and write CD-Rs, and write, read, and rewrite CD-Es.
Industry negotiations over the new digital videodisc (DVD) format have generated a great deal of publicity. The agreed-on standard format will provide both video distribution and digital storage. The video format will use the MPEG-2 video-encoding scheme with digital surround sound. The disc will have the same physical characteristics as CD-ROM and CD-R, with a diameter of 120 mm, Constant Linear Velocity (CLV) sector layout, and Reed-Solomon error correction. Higher laser power will allow a shorter pit length and track pitch (0.74 micron). Four configurations will provide from 4.7 to 17 GB capacity, using multiple layers and double-sided discs.
These new discs will require new readers. However, the new readers will
be backward-compatible with CD-ROMs. There is still some question about compatibility with CD-R media. Plans also include a Super Density Recordable (SD-R) disc that will store 3.8 GB single-sided and 7.6 GB on a double-sided disc.
While these new technologies promise enormous savings in storage cost and a new generation of high-quality multimedia products, they are still a few years away from the consumer market. Meanwhile, market projections show the cost of CD-R recorders dropping to $300, and the cost of CD-R media to $2 per disc, by 1998. This will allow the technology to compete with magnetic tape systems as a primary backup device. The boom in CD-ROM reader sales and increased competition in the CD-R recorder industry are bringing prices to a level where a small organization or even an individual can take advantage of the benefits of, yes, recording CD-ROMs.
Where to Find
Audio Development
West Des Moines
, IA
Phone: (515) 221-1333
Fax: (515) 221-1365
CD Associates
Irvine, CA
Phone: (714) 733-8580
Fax: (714) 453-0868
Clover Systems
Laguna Beach, CA
Phone: (714) 499-9566
Fax: (714) 499-4844
Corel
Ottawa, Ontario, Canada
Phone: (800) 394-3729
Fax: (613) 761-9176
Creative Digital Research
San Jose, CA
Phone: (408) 255-0999
Fax: (408) 255-1011
Eastman Kodak
Rochester, NY
Phone: (800) 235-6325
Elektroson
Bala Cynwyd, PA
Phone: (610) 617-0850
Hewlett-Packard
Palo Alto, CA
Phone: (800) 810-0134 or (970) 635-1500
Incat Systems
Campbell, CA
Phone: (800) 774-6228
Fax: (408) 379-2409
JVC Information Products
Irvine, CA
Phone: (714) 261-1292
Fax: (714) 261-9690
Meridian Data
Scotts Valley, CA
Phone: (800) 767-2537 or (408) 438-3100
Fax: (408) 43
8-6818
NSM Jukebox
Bensenville, IL
Phone: (708) 860-5100
Fax: (708) 860-5144
Optical Media International
Los Gatos, CA
Phone: (800) 347-2664
Fax: (408) 376-3519
Philips Electronics
San Jose, CA
Phone: (800) 235-7373 or (408) 453-5129
Fax: (408) 453-0680
Pinnacle Micro
Irvine, CA
Phone: (800) 553-7070 or (714) 727-3300
Fax: (714) 727-1913
Pioneer New Media Technologies
Long Beach, CA
Phone: (800) 444-6784
Smart Storage
Andover, MA
Phone: (508) 623-3300
Fax: (508) 623-3310
Soliton Computing
Redlands, CA
Phone: (909) 307-3377
Fax: (909) 307-3379
Sony Electronics
San Jose, CA
Phone: (800) 352-7669 or (408) 432-1600
Yamaha Systems Technology
San Jose, CA
Phone: (800) 543-7457 or (408) 467-2300
Fax: (408) 437-8791
Young Minds
Redlands, CA
Phone: (
800) 964-4964
HotBYTEs
- information on products covered or advertised in BYTE
illustration_link (12 Kbytes)
Premastering transforms raw input files into an image of the eventual CD. Some software allows simulation of the CD.
photo_link (23 Kbytes)
JVC's Personal RomMaker internal CD-R drive records and plays CDs at speeds of up to 4X.
Jason J. Hyon is a project leader at the Jet Propulsion Laboratory in Pasadena, California. You can contact him on the Internet at
jason.j.hyon@jpl.nasa.gov
. Michael D. Martin is a member of the technical staff at the Jet Propulsion Laboratory. He is the project engineer of NASA's Planetary Data System and task manager for the Data Distribution Lab.
CD It for Yourself
