Optical Discs: CD, DVD, HD-DVD, Blu-Ray and everything else that's shiny and spinning!

Types of Optical Discs 

• CD
  CD, which as we all know stands for Compact Disc, is the first and most common type of optical disc. From a collaborated effort between Philips and Sony in the 80s came a sound replacement for vinyl records. So when we talk about CDs, the first thing that comes to mind is music.
• CD-ROM
  The CD-ROM came out in 1984, under the specifications described in the "Yellow Book" (CDs had the "Red Book"). ROM stands for Read-Only Memory. CD-ROMs became even more useful because they were no longer limited to storing audio data but also computer software, encyclopedias, and even games. Later on, the "Green Book" was released to signal that CD-ROMs could now support graphics and mix audio, video, and data all at the same time.
• CD-R
  CD-Recordables, which were originally called CD Write-Once (WO), are just like CD-ROMs in that they can be written to only once. But instead of aluminum coating, CD-Rs use either silver, silvery alloy, or gold coating. They are also cheaper to make.
• CD-RW
  If CD-Rs and CD-ROMs can only be written to once, then CD-ReWritables can be written to a number of times. They are only a bit more expensive than CD-Rs and are catching up quickly. To make the a CD rewritable, it has a special alloy that can switch between two states (cystalline and amorphous) to record the data in. The laser that writes the data also switches between different power levels to write and read data.
• DVD
  DVD stands for "Digital Video Disc" or "Digital Versatile Disc". Unlike ordinary CDs, which can only hold around 700 megabytes of data, DVDs can store a whopping 4.7 gigabytes! This is achieved by (a) storing data onto smaller pits; (b) packing pits and holes on the surface of the disc closer together; and (c) using a laser with a shorter wavelength.
  
  There are even more types of DVDs out there: aside from the single-layer 4.7GB discs, we have single-sided dual-layer (8.5GB), double-sided single-layer (9.4GB), and double-sided dual-layer (17GB) DVDs.
  
  Aside from storage, DVDs also have other types according to purpose/format: DVD-Data, DVD-Audio, DVD-Video, DVD-R, DVD-RW, DVD+R, DVD+RW, DVD-RAM (Random Access Memory), DVD-VR, and DVD+VR.
• HD-DVD
  HD-DVD stands for "High Density Digital Versatile Disc" or "High Definition Digital Video Disc". Single-sided HD-DVDs can store 15 GB while Dual-sided HD-DVDs have 30 GB. There's also a Triple-sided HD-DVD, which holds 45 GB. It can read and transfer data at a speed of 36 Mbps. IT companies leading the HD-DVD push include NEC, Sanyo, the DVD Forum, Microsoft, and Intel.
• Blu-ray
  Blu-Ray discs are named after the color of the laser with a 450 nanometer wavelength. Single-sided discs can hold 25 GB while dual-sided ones stores 50 GB. Its transfer rate is 54 Mbps. While these figures are all better than its main competitor, the HD-DVD, Blu-Ray discs are more expensive to make. Nevertheless, they are backed by Sony, HP, Dell, Pioneer, Philips, Panasonic, Samsung, Apple, LG-Electronics, and Mitsubishi Electric, to name a few!
• Other Optical Discs
  We're not done yet! There are so many types of optical media out there that we've lost count:
  Laserdisc
  Magneto-Optical Disc
  Fluorescent Multilayer Disc/Card
  Digital Multilayer Disc
  Ultra Density Optical
  Professional Disc for DATA
  Versatile Multilayer Disc
  Holographic Versatile Disc
  Tapestry Media
  Read more about the other types of optical discs.