are out of focus, and thus not detected by the reading spot. As a result, the CD/DVD method offers a great resilience against disc anomalies, offering great playability. Low information density. According to the patent specifications the spot diameter is around 10 micrometres. Thus, the areal information density is, according to the patent specifications, around a factor hundred less than that of a regular CD. This amounts to a capacity of 5 Mbytes for a disc of 12 cm diameter. The inevitable downside to this is that Russell's disc offers playing time less than one minute of digital CD sound. In case we have digital video at 30 Mbit/s, as claimed above, Russell's disc would be read in less than two seconds. How such extremely fast scanning could be implemented was not disclosed. Photographically copying of data. The patents do not address any details of the digital coding techniques used and/or details of methods how to solve the problems associated with extremely high bit rates of digital video signals. Due to limitations of electronics circuitry, there was no (MPEG) source coding at the time to lower the overall bit rates. The uncompressed bit rate of a color video signal is around 200 Mbit/s, and it is far from clear how the mechanical (scanning speed) and electronic challenges imposed by these enormous bit rates were solved. The patents do not mention error correction or other digital coding technology. See also David Paul Gregg Optical recording References External links 1931 births American inventors Living people Reed College alumni