characteristics of software.

<pre> The software is a logical rather than physical system component. Therefore, the software features that are significantly different from those of hardware: 

1. The software is developed or engineered, it is not available in the classic sense. 

Although there are some similarities between software development and hardware production, two activities are fundamentally different. The two activities, we have quality as defined by the program? An excellent book of essays on software operation, Tom DeMarco claims [DEM95] counterpoint. He said: "Instead of asking:" Why does software cost so much? "We must begin by asking" What have we done to allow the software today, it costs so little? "The answer to this question will allow us to continue the extraordinary level of achievement that continues to distinguish the software industry." The software was designed and manufactured. commitment was achieved through good design, and production phase, the hardware may introduce problems related to quality, the software is not able (or easily corrected). Both activities rely on people, but relations between the executive and work to implement a completely different . Both activities and the need for "product", but the different approaches to construction. The cost of the focus of software engineering. This means that projects can be managed as projects of manufacturing software.

 2 The software does not "wear out".

the failure rate as a function of the hardware of the time. Relationship, often referred to as "bath curve" indicates that the hardware is the relatively high failure rate in the world (the faults are often associated with the design flaw or manufacturing), the fault is corrected and the level of failure rate falls steady-state (ideally, the choice is relatively low) for a while. Over time, however, increases again as the failure rate of hardware components suffer the cumulative effects of dust, vibration, abuse, extreme temperatures can, and many other environmental ills. Suffice to say, the hardware begins to wear. The software is not sensitive to the environmental problems that cause equipment wear. In theory, therefore, that there must be no rate curve software to be in the shape of the curve "idealized" .ndetected failures will cause high failure rates in the life of the program. However, they must be corrected (ideally, without introducing other errors), and the curve flattens idealized curve exceeds the gross shown.The real failure of the models (see section 8 for more information) to for the software. However, it is clear that indirectly, the software does not wear out. But it is getting worse! This is clearly contrary to the best explanation "real curves" feature shows wear on the difference between hardware and software. If a hardware component wears out, replacing it with spare parts. There is no software spare parts. All software failure indicates an error or a design process to transfer the design of executable machine code. So involved, software maintenance is much more complex than the hardware maintenance. 

3 Although the industry is moving towards fulfilling its core component, the software is still more personalized. 

Consider the manner in which the control hardware for computer-based products and building design. design engineer draws a simple diagram of digital circuits, doing some basic analysis to ensure that the appropriate function to achieve, then go to the shelf, a catalog of digital content. Each integrated circuit (IC or chip called), part number and interface validation, functional well-defined..