short section of molecule that is generally perceived to be related to the production of a specific protein. If we think of these distinct segments as illustrative of contexts, then there is a very strong parallel to computer memory. While at its most basic, computer memory appears as a string of individually addressable words filled with bits, in fact we can layer a much more complex information organization on top of this. For example, by designating a section of memory to the task of defining further subsections, where they start, their extent and some general way to refer to them, then we can create a file system on top of a linear memory structure. The files give us the first level of decomposition into discrete contexts. We can make the various contexts even more specific by not only organizing the way that we reference memory, but by assigning specific procedures in the form of distinct sets of computer code to interpret specific segments of memory. Consider, for example the recording of music within the domain of a computer.

Music is a complex rendition of sounds that are conveyed from source to destination by way of acoustic waves that propagate through various materials. The sensori-motor experience of a computer central processing unit does not encompass sound; it encompasses words containing bits. Consequently, to remember music, a computer needs to detect the acoustic wave form and to translate this into the sensori-motor representation form of a central processing unit by digitally sampling the acoustic waveforms of music, and by doing this, create a stream of words and bits that can be stored in a mechanical device through an electromagnetic based process. When these words and bits are retrieved, the context of the original music must also be retrieved and reestablished, thus allowing, through translation, the bit streams to be re-cast as acoustic waveforms emanating from a speaker. Now, we hear once again the original music. In a similar fashion, a series of words and bits can be recorded that derive from visual images.

The mechanisms through which computers store information, including sets of instructions that tell the central processing unit of the computer what to do with that information, are termed memories. We use plural of the term advisedly in that there are several memory technologies, which offer different characteristics to the overall computer architecture. From an historical perspective, memory has been a major area of evolution of electronic computer systems since their inception in the 1940’s. Variants for computer memory that we can introduce now, but which we’ll explore in more detail in later sections, are, among others: read-only memory, random access memory and bulk memory such as disk drives and magnetic tape.

We have noted that just about all computers today have a so-called Von Neumann architecture, where instructions and data are contained in memory, and a processing unit reads the instructions and executes them on the data. Computers also have input/output channels that give them access to the outside world. Each channel typically has its own processing capabilities, dedicated to the management of the flow of information in and out of the computer through that channel. Let us consider three examples.

A print channel allows sending information from the computer to a printer. It is essentially an output channel, since the main flow of data goes from the computer to the external device. However, it is also an input channel because the printer may send data back to the computer, for example a signal indicating that it doesn’t have any more paper. A small unit of processing capability links the computer and the printer and manages the flow of data and signals, moving information between the memory of the computer and the memory of the printer when the signals show readiness. One equivalent of the printing example by computers might be singing by humans. In singing, the main flow of information within the singer goes from the brain to the buccal system, which itself governs the various anatomical maneuvers that lead to the expression of the song. A feedback system is capable of signaling, for example, an echo, or other acoustic

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