Optical drives

How It Works: DVD

How It Works: DVDOur primer on Digital Versatile Disc, better known as DVD: How it works and what you'll need to use it.Andrew Brandt

Digital Versatile Disc (DVD): a high-capacity optical storage medium for video and data.

  • Discs hold about seven times as much information as CD-ROMs.
  • May require special hardware.
  • Development of recordable DVD format stunted by standards war.

    • You've seen people watching Austin Powers on their laptops. But with Digital Versatile Disc, aka DVD, you can do more than watch movies: You can also store gigabytes of data and run multimedia applications. DVD's 4.7GB of storage far surpasses that of CD-ROM's 650MB, though the discs are the same small size. Within the next few years, DVD-ROM drives will likely replace CD-ROM drives on most new computers.

    DVD comes in two formats: DVD-Video (also known simply as DVD), which is used for movies, and DVD-Read-Only-Memory, which is used for data storage. DVD movie players, which vendors hope will supplant VCRs in home entertainment systems, can't read DVD-ROMs. But DVD-ROM drives that ship with computers can read DVDs, CDs, and DVD-ROMs.

    Like CDs, DVDs store data in microscopic grooves running in a spiral around the disc. All DVD drive types use laser beams to scan these grooves: Minuscule reflective bumps (called lands) and nonreflective holes (called pits) aligned along the grooves represent the zeros and ones of digital information.

    But that's where the similarities end. DVDs use smaller tracks (0.74 microns wide, compared to 1.6 microns on CDs) that allow them to store more data. The narrow tracks require special lasers--which can't read CD-ROMs, CD-Rs, CD-RWs, or audio CDs. DVD-ROM drive makers solved the problem by putting two lasers in their drives: one for DVDs, the other for CDs.

    Recording-capable DVD drives let you store data on special discs called blanks. When the recording laser in these drives hits the light-sensitive material on the disc surface, tiny reflective blocks become nonreflective, like the pits on commercially pressed DVDs.

    There are currently four standards for recordable DVDs (see Recordable DVDs Compared chart). DVD-Recordable is a write-once standard; first-generation DVD-Rs could hold 3.95GB of data but can now hold 4.7GB. DVD-R drives cost about $5000, so they're best suited for professional uses such as developing DVD-ROM titles.

    The three other standards let you record on a disc more than once. DVD-RAMs come in cartridges and hold 2.6GB per side. The DVD Plus Rewritable, or DVD+RW, format holds 3GB, and 4.7GB versions are in the works. Pioneer's DVD-Rewritables (DVD-RW) store 4.7GB.

    Among these rewritable formats, only DVD-RAM is available to consumers. It's favored to become tomorrow's replacement for both the VCR and CD-RW.

    Coming Soon to a PC Near You

    DVD's time has come--almost. According to analysts at International Data Corporation, DVD-ROM drives are expected to overtake CD-ROM drives as standard equipment on home and notebook PCs by 2001. But in the meantime, CD-ROM drives are still expected to outsell DVD-ROM drives 105 million to 22 million this year.

    DVD-ROM drives fit into the same PC drive bays as CD-ROM drives. They have been optional in new PCs from just about every PC maker for the past year. Vendors including Hi-Val, Philips, and Sony sell external models; kits that include software and hardware decoders for MPEG-2 video run about $200 to $300. In 1999 PC makers started shipping more notebook computers with DVD-ROM drives, as fixed or removable devices. You can also buy third-party drives for notebooks that connect through the PC Card slot.

    DVD-ROM drive read speeds--or "X" speeds--differ from those of CD-ROM drives. A first-generation 1X DVD-ROM drive reads discs at about 1.3MB per second and reads CD-ROMs at roughly the same speed as an 8X or 9X CD-ROM drive. The 4X and faster DVD-ROM drives commonly sold today read CD-ROMs at about the same speed as a 32X CD-ROM drive. Because of the paucity of DVD-ROM apps, the biggest benefit of buying a faster DVD-ROM drive is better CD-ROM performance.

    If you have a processor slower than 300 MHz, you may want to get an MPEG-2 decoder card to watch DVD movies and run multimedia apps. Video is stored on DVDs with MPEG-2 compression. For the video to run, the data must be decoded, which requires lots of processing power; too little can mean dropped frames. An MPEG-2 card, which sells for $25 to $50, takes over the decoding work for the processor, allowing the video to play smoothly.

    MPEG-2 decoders also typically offer a TV-out connector, which lets you watch DVD movies on a TV. Some new PCs include these decoder cards, while others include a TV connection jack on their video cards. If you want to watch full-screen movies on an underpowered notebook equipped with a DVD-ROM drive, you might need a PC Card MPEG-2 decoder like Margi's DVD-to-Go.

    While DVD-ROM drives are positioned to replace CD-ROM drives, recordable DVD faces a stiff challenge from recordable CD formats, especially CD-RW. Drive vendors have divided into four camps, each supporting one of the four standards for recordable DVD. DVD-R hardware is sold exclusively by Pioneer, and the drives cost about $5000; DVD-R blanks, made by Pioneer and TDK, cost about $45 a pop. DVD-RAM drives from Panasonic, Toshiba, and Hitachi cost $300 to $700 and the discs sell for $25 each. DVD-RW drives from Pioneer have appeared only as consumer-electronics devices costing about $2400, with discs running $30. Finally, Sony, HP, Yamaha, and Philips back DVD+RW but haven't yet released products.

    At the moment, DVD-RAM is leading the recordable race. However, only users who need storage with extremely high capacity are turning to it. Most consumers who need optical storage find that CD-RW drives fit their needs much more affordably. According to IDC analysts, recordable DVD drive sales won't pick up until more drives capable of reading recordable DVDs hit the market.

    Additional Resources:

  • DVD Forum
  • The DVD FAQ
  • A Closer Look at DVD

    • Andrew Brandt is an associate editor for PC World.    Recordable DVDs Compared (chart)

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