DVD-RAM is a high-capacity,
high-performance optical disk that allows data to be read, written and
erased. It is designed to work exactly like a floppy disk, allowing
users to copy and delete files from it, and use it to run programs.
DVD-RAM offers all of the benefits of DVD including high capacity
and compatibility with CD formats combined with enhanced rewriteability.
With current capacities
of 2.6GB to 5.2 GB per disk, DVD-RAM offers up to eight times the storage
of a rewriteable CD. The growth path for DVD-RAM takes capacities even
higher to 9.4GB per disk. In addition, DVD-RAM is much cheaper than
conventional magneto-optical drives. At less than one penny per megabyte,
it is the most economical rewriteable medium available today. Also,
it can read all of the CD and DVD formats including CD-ROM, CD-Audio,
CD-R , CD-RW, DVD-ROM and DVD-R, making it an ideal choice for high-density
data storage and exchange.
DVD-RAM drives use
phase-change technology in which a laser heats the inner surface of
the disk to magnetically charge it. This allows the data to be rewritten
hundreds of thousands of times. A "wobble-land-groove" format
provides clocking data, with marks written on both the grooves and the
lands between grooves. The grooves and pre-embossed sector headers are
molded into the disc during manufacturing. The DVD-RAM wobble-land-groove
format or track structure makes DVD-RAM technology reliable, and the
constant linear velocity format provides high access speed and capacity.
DVD-RAM discs consist
of double layers of metallic film embedded in hard plastic. The drive
motor constantly changes the disc's rotational speed to compensate for
the location of data on the disc. A laser uses light of varying intensities
to write and erase data. The metallic layers in the disc are made of
a crystalline material that reflects light the way a mirror does. To
write data, the laser heats a metallic layer to 900 to 1,300 degrees
Fahrenheit and creates pits in the surface. To erase or change data,
a weaker laser beam heats the pits to approximately 400 degrees Fahrenheit.
discs come with or without cartridges and can be read by some "newer
generation" DVD-ROM drives (check your drive's specification for
additional info). There are two types of cartridges: type 1 is sealed
and type 2 allows the disc to be removed.
single-sided DVD-RAM discs hold 2.6GB of data. Expected to be available
in Q4 99, single-sided 4.7GB DVD-RAM disks achieve their high storage
capacity from a decrease in track pitch and pit lengths, allowing for
a higher density media. Today, the minimum pit length of a single layer
DVD is 0.4 micrometers, as compared to 0.83 micrometers for a CD. In
addition, the DVD track pitch is reduced to 0.74 micrometers, less than
half of CDs 1.6 micrometers. With the number of pits equating to capacity
levels, DVD's reduced track pitch and pit size creates four times as
many pits as CDs.
The transfer rate
for DVD-RAM is determined by the media specification. The 2.6GB disc
has 1,385KB/sec. transfer rate, and the 4.7GB disc will have 2,770KB/sec.
transfer rate. Access times will also evolve with an increase in disc
rotational speed, reducing drive latency. Further reductions in access
time will come from mechanical improvements, a more robust servo technology
and mass reductions in the optical pickup.
Several DVD formats
were developed and standardized by the DVD Forum to meet a variety of
write-once and rewriteable needs. These formats include DVD-RAM, DVD-R,
and DVD-RW. The following table summarizes the differences between these
While there are
specific areas for which DVD-R and DVD-RW are best suited, DVD-RAM is
the only writeable DVD standard that will fulfill the requirements of
mass commercial and consumer audiences. DVD-RAM differs from the other
writeable DVD standards in several ways. Firstly, it provides random
access rewriteability, like a floppy disk drive, making it perfectly
suited for use and re-use by consumers. The low cost of both the drive
and media make it a natural choice for a wide audience of users, even
those that are value-conscious. With support by the DVD Forum and a
strong feature-set, DVD-RAM is anticipated to continue as the leading
DVD-RAM drive shipments
began in 1998, and more than 100,000 units were shipped that year. Research
firm Disk/Trend expects phase change drives to be displaced by DVD-RAM
drives after 1999, and DVD-RAM to begin its run as the dominant product
in 1999. Disk/Trend predicts that DVD-RAM will remain the dominant DVD
rewriteable format due to its current market predominance, with major
growth beginning in 2000.
From Backup to Publishing
DVD-RAM is designed
to playback all DVD-ROM applications as well as for desktop storage,
data exchange, backup and archiving. Because of the wide variety of
suitable applications, a DVD-RAM drive could be used as a viable replacement
to do the job of several other devices, such as CD-ROM, CD-R, optical
disk, tape, removable hard drive and floppy drive storage.
DVD-RAM is an excellent
choice for backup and archiving. At less than a penny per megabyte,
cartridges are extremely inexpensive. Given the well-established durability
of optical media, they are also far more reliable than tape, the only
cost-competitive alternative. And, because cartridges can be stored
on the desktop, adding to archives or retrieving files from backup is
infinitely easier than doing so from tape.
With their high
capacity and rewritability, DVD-RAM discs have enormous potential for
many markets, such as education and entertainment. They are also ideal
for personal multimedia publishing, in applications such as presentations,
sales tools, training and corporate communications. Future set-top box
applications, which will give users the capacity and bandwidth to download
their favorite movies, are also on the horizon. DVD-RAM drives are already
being introduced in some personal video recorders as an alternative
to tape. In addition, new DVD-RAM jukeboxes provide high-capacity, on-line
storage for applications such as document imaging and image management.
Because they follow
a standard format, all DVD-RAM drives and cartridges will be compatible
with each other. This compatibility will further drive down prices,
making the technology even more appealing to OEMs and consumers.
A DVD Forum approved
format, DVD-RAM is a storage medium with a unique position in the high-capacity
storage arena. It offers the "average" consumer an opportunity
to afford high-capacity, rewriteable, removable storage for the first
time. With the ideal mix of features at an affordable price point, DVD-RAM
is well-positioned to become the medium of choice for high-density storage
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