On Windows, or any other operating system, it's somewhat complicated to know how long a PC has been on , since it's clear there's no application that displays this information. Perhaps the developers consider it unnecessary, or perhaps they simply never thought to develop such a utility, which, upon closer examination, could be very useful for parents, for example, who want to know how many hours their children have spent on the computer. Fortunately, on Windows we can now find this out using a program specifically designed for this purpose: Windows Elapsed Running Time.
Windows Elapsed Running Time is a small utility that displays the time elapsed since Windows started. Its compact interface takes up very little space on the desktop, so you can always have the time displayed in days/hours (minutes and seconds) available. Furthermore, once launched, you can close it immediately if you wish, as it also resides in the system tray, where it will always be visible simply by hovering your cursor over it, and from where you can, of course, manage it.
Among the configuration options offered by Windows Elapsed Running Time are displaying the hours or days as an icon in the taskbar, as well as automatically loading the program every time Windows starts, among others. Although it's only available in English, learning to use it won't be a problem; all you need to do is run it…
Windows Elapsed Running Time is completely free and portable; it requires no installation. Simply extract the files and run the small executable file. An installable version is also available. It supports all versions of Windows 7, Vista, XP, 2003, etc.
Official site | Download Windows Elapsed Running Time (237 KB – ZIP)