You probably already know the background on the types of DVD and Blu-ray Discs (BDs) out there. In case you need to explain it to a co-worker, relative (like your stupid brother), or a neighbor, I’ve gathered some of the details here for you to pass along.
The CD or compact disc started it all back in the early 1980s when we put our scratched-up analog LPs aside for the new digital and crisp-sounding music CDs. At the time, it was said that, to the ear, the leap in performance was greater than the leap from black and white TV to color was to the eye. Since it was a digital format, versions of the CD were made for computing. Back when floppy discs carried a whopping 1.44MB of data, the 650MB that CD-ROMs brought seemed incredible.
Pronounced CD “dash R”—not “minus R”—recordable CDs (CD-R) came along in 1988. They use a dye coating to record the ones and zeros. As the laser burns pits into the dye, they become opaque and reflect less light than unburned areas, creating the distinction between ones and zeroes. The writing process is permanent once the recording session is closed. In 1997, CD-RW was released using an alloy that can change back and forth from a crystalline form. This process required a more sensitive playback device since the light-absorbing areas are less distinct from the nonabsorbing areas. The CD-RW method uses phase change technology where the degree of reflection reached is only 15% to 25%, compared to the 40% to 70% reflection from CD-R discs. Mostly because of these reasons, there were compatibility issues among the different disc types, but these issues have mostly gone away with newer “combo” drives. One thing to be aware of is that not all older drives can handle the different formats, so it always pays to check.
NEWER AND BETTER
Like most things technological, CD-ROMs soon gave way to a newer and better disc media called DVD. Although some claim it stands for Digital Video Disc or Digital Versatile Disc, it apparently does not really stand for anything at all, according to the standards-setting DVD Forum. DVDs came on the scene in 1997 and developed much along the same path as CDs, only instead of getting started in music, DVDs delivered movies and videos.
The DVD brought a sizable increase in capacity and capability. The storage capacity increased to 4.7GB due to a shorter-wavelength laser (650 nm versus 780 nm) and smaller pits or burned areas (0.79 µm versus 1.6 µm), allowing higher data density. DVDs are also much faster in achieving 1,350 KB/s data transfer rates (at x1 speed) compared to 153.6 KB/s for CDs. Much like the VHS versus Betamax wars in the 1980s, there were two leading formats for the new discs. When one camp approached IBM for backing, the company stepped back, assembled an expert panel, and declared a boycott of both until a converged standard could be achieved. And they did—calling the new standard DVD at the end of 1995. Part of the compromise included using a modulation technique called EFMPlus, which is better suited for dealing with disc damage like fingerprints and scratches. However, it is 6% less efficient and brought the target 5GB storage capacity down to 4.7GB. With widespread industry support, the DVD became the most successful consumer electronics product of all time in less than 3 years of its introduction. In 2007, only 10 years after introduction, there were more than one billion DVD playback devices in the world.
Mass-produced DVDs or DVD-ROMs are stamped with the data pattern as a read-only media. They are made with a spiral groove starting at the center. DVDs start with a nonrecordable area called the Media Identification (MID) code. The MID contains information identifying the manufacturer and model, byte capacity, and allowed data rates, among other things.
Today, there are six main types of DVDs. Similar to the CD-R, the DVD-R is a recordable disc allowing one burn session that can later be read as a DVD-ROM. DVD-RW and DVD+RW came out in 2001 as rewritable discs able to be recorded, read, erased, and rerecorded more than 1,000 times. The main differences between -RW and +RW boils down to recording process and data formats. As with CDs, DVDs at first were initially unable to be recorded in the other’s format. Today, disc players should be able to use all formats, but again, it still pays to check your drive’s format and get the corresponding disc format.
IT STORAGE AND BACKUP
Adopted more by the IT crowd, DVD-RAM (released in 1998) is a third format for recording, storing, and reading data. Instead of one long spiral groove where the data resides, the DVD-RAM is closely related to hard disc technology where the data is laid out in concentric tracks. Therefore, DVD-RAM does not need any special intervening software to read/write like the packet reading/writing routines for other formats. The DVD-RAM has much faster access, can be reused 100,000 times, and lasts 30 years. These are the kinds of attributes that make the DVD-RAM better suited for general IT storage use like backup and archival.
Not allowing the DVD technology to rest, a format split occurred in early 2000 for DVD-R. The authoring version—called DVD-R(A) using a 635-nm laser—was intended for professional use. The general version, or DVD-R(G), was intended for home use and uses a cheaper 65-nm laser. DVD-R(A) discs are not recordable in DVD-R(G) drives and vice versa, but both can be read in most drives and players.
DVD+R, a write-once variation of DVD+RW, appeared in mid 2002. It is a dye-based medium like DVD-R, and it has a similar compatibility as the DVD-R.
Discs have different speed ratings due to different write protocols and media formulations for faster speeds. Also, higher-power lasers will enable it to move across the media much faster. Matching the speed rating of the disc to the speed rating at which you burn will give the best results. You can get the best results by using discs that are rated at or above the speed of your drive. For example, if you have a 4x drive, you should use a 4x or faster disc. If you want to use up your blank 1x or 2x discs, be sure to set the drive to record at 1x or 2x speed.
A Blu-ray Disc holds 25GBs per layer using a 405-nm blue-violet laser. BD emerged in 2006 and is only slowly picking up speed, mostly due to overall costs. Other BD capacities are 50GB for double layer, 100GB for triple layer, and 128GB for quad layer discs. A BD also comes as BD-R for a write-once-read-many version and a BD-RE for a rewritable version.
It appears that disc media will be around for a long time. One estimate for a multi-laser, multilayer format from Australia called 5D DVD says that we will have a 10TB disc available by 2019. Now we’re getting somewhere!
Jeff Kabachinski, MS-T, BS-ETE, MCNE, has more than 20 years of experience as an organizational development and training professional. Visit his Web site at kabachinski.vpweb.com. For more information, contact .