DVD : A new Standard for Digital Video and Data Storage Colin F Hughes Phd, BSc(Hons), MBCS, MIEEE (Authored 18th June 1997) 1. Introduction Optical media technology has been in existence since the late 1970's. Examples of this are audio CD and video based Laserdisk produced by Phillips. Technological and market trends show an increase in the use of optical media. The majority of software providers perceive optical media as a standard distribution media and hardware suppliers regard it as standard inclusion in any new system. The first CD-ROM was pressed in 1982. Standards such as ISO 9660 'High Sierra' have been in place from the late 1980's. All CD-ROM drives are manufactured to read and write this ISO standard. Hence produced disks will be readable on a variety of platforms. This is of importance to organisations providing multi-platform solutions. 2. The Limitations Now that CD-ROM is well-established as a data storage medium it's physical limitations are driving new advances in optical storage. The two main areas that are being addressed are : Data transfer speed (basic CD ROM drives provide a transfer rate of up to 156Kb/sec), now ten speed drives manufactured by Plasmon are able to increase the data transfer rate. Capacity is restricted to about 650Mb. This equates to 70 minutes of video imagery at a slow bit rate, unacceptable for the entertainment industry. 3. The Solution DVD (Digital Video (or Versatile) Disc) is destined to be the next optical technology to supersede CD-ROM. Initially the format was derived for the entertainment industry. Ideas from the original CD storage mechanism is merged with the latest 1990's storage technology. This involves, reducing track size, using a shorter wavelength laser and relying on a more efficient error detection and correction technique. DVD has a basic storage of 4.7Gb (this is seven times the original CD). Physically DVD and CD-ROM look the same (hence current CD-ROMs should be backwardly compatible with DVD drives). However DVD discs spun at three times the speed. This correlates to a data transfer rate of 1,108K/sec, compared to basic CD-ROM of 153.6K/sec. Additionally DVD can hold up to 133 minutes of MPEG-2 video with three encoded soundtracks (can be coded with Dolby's 5-track surround-sound AC-3 standard). This extra capacity is achieved from reducing track pitch from 1.6 micrometres to 0.74 and inter pit spacing has also been halved (from 0.85 micrometres to 0.4 micrometres). Previous CD-ROM speed was dependant upon infrared lasers. Now visible light semiconductors mass producing a wavelength 650nm and 635nm can read these smaller features. New data encoding techniques more efficient data storage. Solomon Product code (RS-PC) error correction gives an efficiency of up to ten times that of previous error correction/detection on current CD system. The expectation is that DVD technology will be initially driven by the entertainment industry. The first products from this technology are expected early 1997. However it is likely that the drive reliability will increase and prices fall before the technology is a 'defacto' standard in the optical storage industry. 4. CD-ROM vs DVD : A Comparison Please find detailed below a comparison between DVD and CD-ROM technology : Feature CD DVD Disc Diameter (mm) 120 120 Disk Thickness (mm) 1.2 1.2 Disc Structure single substrate two bonded 0.6mm substrates Laser Wavelength 780 (infrared) 650nm and 635nm (red) Numerical Aperture 0.45 0.6 Track Pitch (micrometres) 1.6 0.74 Reference Speed (m/sec) 1.2, CLV 4.0,CLV Number of Data Layers 1 1 or 2 Data Capacity 650Mb (approx) 4.7Gb(one layer) 8.5Gb(two layers) Reference User Data Rate 153.6 (Mode 1) 1,108 (Mode 1), 176.4 (Mode 2)