In computing, unique set size (USS) is the portion of main memory (RAM) occupied by a process which is guaranteed to be private to that process. The unshared memory of a process is reported as USS.[1]
This concept is used for software running under the Linux operating system.[2] It was proposed by Matt Mackall because of the complications that arose when trying to count the "real memory" used by a process.[3] The concepts of resident set size or virtual memory size (VmSize) weren't helping developers who tried to know how much memory their programs were using.[4]