Sometimes it's useful to know whether the hard disk LED indicator on your computer is flashing. Because if it is, that will explain why the computer might be running slowly, or why it might be an idea not to restart the machine right now.
Trouble is, not all computers are fitted with a hard disk activity LED any more. And even if yours has one, maybe the system unit is under your desk and thus the indicator isn't easy to see.
A simple solution is to use a software-based hard disk activity indicator, and DiskLED is a good one. It runs under Windows XP and above, needs no installation, and the download is less than 1 MB. I've checked the application with VirusTotal and it seems totally free of malware and viruses.
You can download DiskLED from http://www.sepago.de/e/research-development/downloads/diskled. The download link is at the top of the right-hand column. Once you run the program you'll see (if you look carefully) a small black rectangle in your system tray. This is your on-screen disk LED, which will flash green when the hard disk is being accessed.
You can also use DiskLED to monitor other performance indicators on your computer. Read the documentation on the web site for more information, or right-click the system tray icon and choose Configure to see what's available.