General systems theory
Although there are many types of physical system - electrical, mechanical, chemical, etc - the mathematical laws that describe them are often very similar. This observation led to the formulation of general systems theory (GST). In essence, GST is an attempt to capture those features that are common across all systems, and to establish a definition of what a system actually is. Building on the early work on GST, the International Council on Systems Engineering Handbook (INCOSE 2015) defines system as
present_to_all
an interacting combination of elements to accomplish a defined objective. These include hardware, software, firmware, people, information, techniques, facilities, services, and other support elements
Mathematics aside, GST gave rise to a simple visualisation of a system as a bounded region:
While it appears trivial, this representation already identifies the system boundary as a key component of the model. What is within the boundary is part of the system, and what is outside the boundary is not relevant. The concept of the system boundary is important in the definition of a software application, for example, where the application requirements define what is inside and exclude everything else. It is also important in project management where the boundary defines the project scope. Making these things explicit at the planning stage simplifies later work.
The system boundary can be thought of as the limit of responsibility. In the project example, things outside the project scope can be ignored because by definition they are not the responsibility of the project. Neither are they under the control of the project manager. In most cases where the GST concept of a system is applicable, it is what is within the boundary that is of interest. However, by adding a few more details to the general model, its relevance to green computing and other fields related to sustainability starts to become clear.
Fig. 2 illustrates the purpose of the system as a way of processing inputs taken from the environment and delivering its result back to the environment. This view of a system can be thought of as synonymous with a process. Software engineers and other professionals who work with computer systems usually think about the inputs and outputs of their system exclusively in terms of data and information. However, that ignores all of the physical exchanges between the system and its environment. A software system cannot operate without a physical device, and the main immediate input into a that device is the electrical power it consumes. Likewise, its main physical output is heat which is released into the atmosphere using heat sinks and fans.
Computing professionals are familiar with another aspect of systems identified by GST, and that is that any system may be decomposed into a network of subsystems as illustrated in Fig. 3. The diagram is simple visualisation of the definition at the top of the page. Taking the argument made previously, though, it is important to consider whether our picture of a system tells the whole story. If we are entirely focused on the internal working of our system of interest, we may fall into the trap of ignoring its interactions with its environment. That is, the system we are interested in may itself be a subsystem in some wider network.
When thinking about green computing, we need to consider, for example, how the electricity that runs our system is generated. We also need to consider how the device was made and where its basic materials came from. We need to consider the transportation of the raw materials from their point of extraction to the place of manufacture, and then the onward transportation of the finished items from the point of manufacture to the end user.
The final network of relationships is very complex and would take a lot of effort to map in full. This is why the GST model of a system with its fixed boundary is so attractive. It provides a rationale for focusing only on a limited component of the whole picture and leaving it to someone else to think about anything that falls outside the system boundary.
Somebody else's problem
The famous book The Hitchhiker's Guide to the Galaxy by Douglas Adams imagines a piece of technology called a Somebody Else's Problem (SEP) field generator. If an object such as a spaceship must remain hidden, the device can create an SEP around it. The effect is that people passing by simply ignore it as if it wasn't there.