A rewritable optical disc. First used in drives by Panasonic in the late 1980s, the phase change technology was subsequently employed in all major optical drives, including CD-RW, DVD-RW, DVD+RW, DVD-RAM, UDO and Blu-ray. The phase change disc technology was invented by Stanford Ovshinsky, who founded Energy Conversion Devices (ECD) in 1960.
Pure Optical
Phase change discs do not rely on magnetic influence as do hard disks and magneto-optic (MO) discs. In rewritable phase change media, the heat from a short, high-intensity laser pulse turns a bit in the recording layer into an unstructured "amorphous" state, and a medium-intensity pulse sets it to a highly structured "crystalline" state. The two states (0 and 1) cause a change in reflectivity, which is sensed when reading the disc.
In "write-once" phase change drives, such as UDO, the media starts out amorphous, and bits are written by turning them crystalline. Once changed, the makeup of the media prevents the bit from being turned back to amorphous. See UDO, optical disc, PD disc and phase change memory.
Phase Change Writing and Reading
Writing a bit is accomplished by pulsing different intensities of a laser into the phase change layer, which changes the bit between crystalline and amorphous states. The bit is read by sensing the reflected light from a low-intensity laser pulse. The crystalline bit reflects the laser beam, while the amorphous bit absorbs the light.
Phase Change Bits
This magnified UDO disk from Plasmon shows non-reflective amorphous (grey) and reflective crystalline (light/dark) bits. The crystalline area is not a single crystal, but a multi-crystalline region. Due to different crystal alignments and interaction of the beam used to image the material, the reflective bits appear variously light and dark. The different sizes of bits are due to UDO's encoding method. (Image courtesy of Plasmon, www.plasmon.com)
Pure Optical
Phase change discs do not rely on magnetic influence as do hard disks and magneto-optic (MO) discs. In rewritable phase change media, the heat from a short, high-intensity laser pulse turns a bit in the recording layer into an unstructured "amorphous" state, and a medium-intensity pulse sets it to a highly structured "crystalline" state. The two states (0 and 1) cause a change in reflectivity, which is sensed when reading the disc.
In "write-once" phase change drives, such as UDO, the media starts out amorphous, and bits are written by turning them crystalline. Once changed, the makeup of the media prevents the bit from being turned back to amorphous. See UDO, optical disc, PD disc and phase change memory.
Phase Change Writing and Reading
Writing a bit is accomplished by pulsing different intensities of a laser into the phase change layer, which changes the bit between crystalline and amorphous states. The bit is read by sensing the reflected light from a low-intensity laser pulse. The crystalline bit reflects the laser beam, while the amorphous bit absorbs the light.
Phase Change Bits
This magnified UDO disk from Plasmon shows non-reflective amorphous (grey) and reflective crystalline (light/dark) bits. The crystalline area is not a single crystal, but a multi-crystalline region. Due to different crystal alignments and interaction of the beam used to image the material, the reflective bits appear variously light and dark. The different sizes of bits are due to UDO's encoding method. (Image courtesy of Plasmon, www.plasmon.com)
 | Reproduced with permission from Computer Desktop Encyclopedia. Copyright (c) 1981-2009 The Computer Language Company Inc. All rights reserved. |
Additional Resources
- Is "market share" thinking "old school" thinking?
- Is "market share" thinking "old school" thinking?HealthA fragmented market is a healthy market. You can compare it to an ecosystem: a great variety of species is best. Domination of one species poses risks: diseases, plagues.So we can say that the operating system market shows a healthy trend, but is still...
- Discussion threads 2009-05-25
- How this blog saved my life and saved me $100,000
- A few months back, I told you about how my neck had gone bad, really bad. At that time, I was in the middle of a six-month dive into pain, alleviated only by gobbling unwholesome quantities of Percoset. Three weeks ago last Friday, I had an amazing surgery that relieved...
- Blog posts 2008-04-20
- First look at Ubuntu 8.04 "Hardy Heron" beta
- Ubuntu 8.04 "Hardy Heron" has just entered the beta phase of development - and that means another 650+MB download and some good hands-on time with my favorite Linux distro! I first took a look at Ubuntu 8.04, codenamed Hardy Heron, back in February when it was in...
- Blog posts 2008-03-22
- The+SSD+failure+debate
- The+SSD+failure+debateMost SSD doom and gloom writers seem uninformedThey know one thing - that NAND and NOR have erase cycle endurance limitations. Then, they create a whole doom and gloom campaign around that one limitation. It's irresponsible technical journalism. Not only are SSD's super reliable, they are are future...
- Discussion threads 2008-02-27
- A Vista SP1 FAQ
- A Vista SP1 FAQVista SP1 changesGood article. My questions: Does Vista SP1 reduce or increase the number of times the user is asked to confirm an action? Does it still do so by blanking the screen?Standalone?Am I wrong to think that the standalone installer is standalone? That is, self-contained?...
- Discussion threads 2008-02-09
- 2008 Mercedes-Benz CLK550 Cabriolet
- Photo gallery:2008 Mercedes-Benz CLK550 CabrioletThe vast model lineup from Mercedes-Benz ensures that one of its cars will suit just about anyone's needs, but the 2008 Mercedes-Benz CLK550 Cabriolet fits a very narrow niche. The CLK550 is a coupe, offered as a convertible or hardtop. With the convertible version, which we...
- Product reviews 2007-11-27
Neighboring Terms
Premier Vendor Content Whitepapers, webcasts & resources from our Power Center Sponsors
- New Online Dashboard for IT Leaders
-
Read about top issues IT decision-makers face every day, plus get cost-effective solutions to real-life IT problems.
- Learn more >>
- Keep Up With The Latest In Document Management with The DocuMentor.
-
Doc delivers the scoop on today's enterprise content management, printer maintenance, and all other issues related to document management. It's the DocuMentor Blog.
- Learn more >>
- The best support in the Linux business
-
If Linux is going to power your mission-critical applications, you'd better have the best support known to business. Novell was rated the top provider of Linux technical support.
- Learn more >>
- Save time with automated shipping solutions
-
The Business Essentials Guide provides you useful tools and templates to help grow your business and save you time with automated shipping solutions.
- Visit the UPS Business Essentials Guide
SmartPlanet
- Thought-provoking progressive ideas on diverse topics that intersect with technology, business, and life, and matter to the world at large. Visit SmartPlanet
- More from IBM
-
- Innovate your business' process model, play against the market, compete against others on our scoreboards and WIN! Try INNOV8 2.0: A BPM Simulator
- Enabling Real-World Business Transformation through IBM Service Management Read the EMA Analyst Report
