The process mdnsresponder.exe is a component of the Apple Service, which is identified with the Bonjour for Windows software application initially utilized by iTunes because of its music sharing functionality. The mdnsresponder.exe process is a native element of the Mac OS X operating system and is associated with the MDNSNSP.DLL, which was ported for the Microsoft Windows Operating System environment.

The Bonjour Service supported by the file mdnsresponder.exe is also described as a zero configuration networking process that provides an automatic discovery feature for services, devices, and computers that are residing on IP based networks. Mdnsresponder.exe utilizes the industry standard IP protocol, which provides devices with an automatic discovery feature without requiring user intervention (when entering IP addresses) or the need for configuring DNS servers.
Non-system processes like mdnsresponder.exe originate from software you installed on your system. Since most applications store data on your hard disk and in your system's registry, it is likely that your computer has suffered fragmentation and accumulated invalid entries which can affect your PC's performance.

In Windows Task Manager, you can see what CPU, memory, disk and network utilization is causing the Bonjour for Windows Component process. To access the Task Manager, hold down the Ctrl + Shift + Esc keys at the same time. These three buttons are located on the far left of your keyboard.

This process is considered safe. It is unlikely to pose any harm to your system. The mdnsresponder.exe file should be located in the folder C:\Program Files\Bonjour. Otherwise it could be a Trojan.

This process is not considered CPU intensive. However, running too many processes on your system may affect your PC’s performance. To reduce system overload, you can use the Microsoft System Configuration Utility (MSConfig) or the Windows Task Manager to manually find and disable processes that launch upon start-up.

Use the Windows Resource Monitor to find out which processes and applications write/read the most on the hard drive, send the most data to the Internet, or use the most memory. To access the Resource Monitor, press the key combination Windows key + R and then enter 'resmon'.