Software doesn’t “wear out”:
Considering the given figure 01. This is often called the “bathtub curve”. It indicates that, at the beginning of the life of hardware it shows high failure rate as it contains many defects. By time, the manufacturers or the designers repair these defects and it becomes idealized or gets into the steady state and continues. But after that, as time passes, the failure rate rises again and this may be caused by excessive temperature, dust, vibration, improper use and so on and at one time it becomes totally unusable. This state is the “wear out” state.
On the other hand, software does not wear out. Like hardware, software also shows high failure rate at its infant state. Then it gets modifications and the defects get corrections and thus it comes to the idealized state.
But though a software not having any defects it may get the need of modification as the users demand from the software may change. And when it occurs, the unfulfilled demands will be considered as defects and thus the failure rate will increase. After one modification another may get the necessity. In that way, slowly, the minimum failure rate level begins to rise which will cause the software deteriorated due to change, but it does not “wear out”.
In the following given figure 02, the idealized curve for software has been shown. Also the change to failure rate due to users demand and the rise of the minimum failure rate has been shown on the actual curve.