Sometimes we need to know the details of some of our hardware. For example, you need to know the manufacturer of your hard disk drive or the clock speed of RAM (important during upgrade). The Windows 7 default application gives enough information, but for advanced usage (as said above) it is of limited use.
It is also a important tool while buying a second hand computer, to check individual components in branded laptops and desktops; generally they tweak to hide the OEM data.
The above screenshot shows the Windows 7 user has increased the RAM by adding another RAM in the empty slot of a HP laptop. Due to inadequate knowledge, the clock speed of these RAM do not match. Generally it does not cause too much problem, but the optimum performance can not be reached. (Click to zoom the screenshot).
System Information for Windows is a freeware to check all the hardware specifications of your desktop or laptop running any Windows operating system, including Microsoft Windows 7.