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From this it can be seen that 23 seconds of CD-quality digital audio requires the same amount of digital storage or transmission capacity as Tolkien's longest novel! The Compact Disc, a remarkable development by Sony and Philips in 1982, stores 4 Megabytes in only a 6 mm square of its surface area.
However, digital audio is a relatively small data-stream compared to video. Raw video is several hundred Megabits per second, but after MPEG-2 compression (a process of storing the information in a more compact form) the data-rates are still very high. To convey movies and fast-action sports with sound with a quality equivalent to broadcast PAL or NTSC, 3 and 7 or more Megabits-per-second respectively are required. For High Definition TV, 20 or more Mb/s is needed.
The Pace of Electronic Technology Development
The Compact Disc is a rare example of a breakthrough technological development - and successful marketing in the absence of competing technologies - made without the involvement of standards organizations, which was technically highly developed and remains unchanged and in widespread commercial use, many years after its initial design. In contrast, the development of communication and information technologies is generally piecemeal and messy - with competing technologies and commercial considerations, often attempting to retain compatibility with older technologies and standards.
The primary driving force behind the explosion of IT has been the integrated circuit - the manufacture of transistors and other components integrated into a functional circuit all at once using chemical and photographic techniques, in contrast to previous technologies based on assembly of smaller components into larger systems. As optical, chemical and design techniques have improved in the past three decades, progress in creating more and more complex integrated circuits has followed, with remarkable accuracy, the prediction by Gordon Moore - one of the founders of Intel - in the late 1960s, that the economically producible number of transistors on an integrated circuit would double every 18 months.
'Moore's Law', as it came to be known, together with advances in speed, reliability and cost-effectiveness of all electronic components and systems - in combination with advances in design and computer programming - have lead to the continuing explosion of IT, which is so challenging to understand and manage.
The pace of electronic progress continues today - with dramatic progress in fiber-optic communications and in radio, microwave and now satellite technology. In comparison with the hardware technologies, the art and engineering science of computer programming is advancing relatively slowly.
Types of Communication Systems
Basic Communication Principles
Electronic communication systems over distances of a kilometer or more can be approximately classified into three categories:
- Broadcast - eg. such as commercial radio and television
- Point-to-point radio - eg. such as CB radio
- Telecommunications - eg. telephones, fax, Internet, leased lines
While there is a clear distinction between the unidirectional, one to many, broadcasting paradigm with the one-to-one, bi-directional telecommunications paradigm, many communications systems cannot be so easily classified.
A comprehensive or detailed taxonomy of communication systems is not appropriate here. Rather, the intent is to describe the salient characteristics of several important systems as an aid to thinking about electronic communication in general - in terms of the contrasting and in-common techniques and purposes.
Computing and storage technologies, despite their complexity, are often easier to understand because they are physical, complete, systems that can be entirely owned and observed. Communication systems can be harder to understand because they typically involve subtle and invisible physics and inter-working with distant equipment and technical standards which are owned or controlled by large telecommunications carriers and/or governments.
Many of these technologies involve radio waves - electromagnetic waves - perturbations in the electrical and magnetic fields of space which travel at the speed of light - about 300,000 km per second. The frequency of the radio wave determines its wavelength - which directly affects how it travels around physical objects, from features as large as the curvature of the earth to such small barriers such as wet foliage and raindrops. The propagation characteristics of electromagnetic waves (how the radio waves travel through space and past obstacles) determine their useful distance for communication.
For instance if a wire's voltage is made to change from positive to negative and back at a rate of 30 billion cycles per second, it will radiate electromagnetic waves into space. These are not dependent on air - they travel just as well in vacuum - but can be absorbed and reflected by materials which conduct electricity and/or which have magnetic properties. 30 billion cycles-per-second - 30 Giga Hertz or 30 GHz - is close to the limit of electronic circuits at present. As the waves radiate outwards at the speed of light, the distance between the peak of one wave and the peak of the wave which follows it is about 1 cm. Just as long wavelength waves in the ocean or long wavelength low-frequency sound waves wrap around objects in their path, so do the 300 meter long waves of a medium wave AM radio signal. However, 1 cm long waves behave much like visible light (which has a wavelength of about 0.0005 mm) - very little wave energy wraps around the edge of barriers, which reflect or absorb the waves. Consequently, radio communication at 30 GHz generally requires a 'line-of-sight' path between the communicating antennae - in contrast to 300 meter wavelength radio waves, which are only seriously attenuated by such barriers as the largest mountains and the curvature of the Earth.
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