Wirth's Law states that computer software increases in complexity faster than does the ability of available hardware to run it. Another way of stating this is "Software slows down faster than hardware speeds up." This annoying phenomenon results in part from software bloat, the tendency for applications to evolve new features that place ever-increasing demands on computer resources. Wirth's Law is attributed to the Swiss computer scientist Niklaus Wirth, who wrote a paper lamenting software bloat in 1995.
The problem defined by Wirth's Law is not entirely caused by bloated applications. If the operating system on a PC is too advanced for the available memory and processing speed, that computer may run slowly. This can occur, for example, if Windows Vista is installed on an old computer designed for Windows 98. Poor system performance can result from the presence of viruses, Trojans, spyware or severe fragmentation of data stored on the hard disk. A system can also be slowed if the user tries to run too many applications at once, allows too many programs to load at startup or runs a "heavy-handed" system security utility.
Slow computer performance on the Internet can occur because of limited data transfer rate. A dial-up connection is no longer adequate for many Web-based applications. Even a high-speed connection may function slowly if too many users attempt to access a local Internet service provider (ISP) or if a significant number of users are engaged in bandwidth-intensive activities.