A subnotebook (or ultraportable computer) is a small an lightweight portable computer, with most of the features of a standard laptop computer but smaller. The term is often applied to systems that run full versions of desktop operating systems such as Windows or Linux, rather than specialized software such as Windows CE, Palm OS or Internet Tablet OS. The term "ultra-mobile PC" (UMPC) is also frequently used to refer to such machines, although this also refers to a small form-factor tablet PC platform.