ARPCache is a secret, undocumented section of the registry used to store information for Add/Remove Program items in the latest versions of Windows.

If you open Add/Remove Programs in the newer versions of Windows, you will notice that certain information has been added, such as, size, frequency of use, and last used on.

This data is kept in binary files in the ARPCache of the registry, which means that even if you know where it is in the registry, you probably will not be able to read it. ARPCache Viewer deciphers the binary files and shows you what is in each entry.

Some people have mistakenly confused this ARPCache (which obviously stands for Add Remove Programs Cache) with the documented ARP (which stands for Address Resolution Protocol) Cache of the Windows operating system. The documented ARP has to do with resolving IP addresses across networks. This has nothing to do with the ARPCache in the registry.

A problem with the ARPCache is that Windows automatically adds to this storage area but it does not automatically remove items when they are uninstalled. The ARPCache can be used to clean out the ARPCache or a good registry cleaner, like, RegVac, can be used.