Microsoft last week revealed how it will squeeze Windows 8.1 onto devices with storage space as small as 16GB to fulfill a promise earlier this year that OEMs could produce low-cost tablets and laptops. The technology Microsoft will use, dubbed "WIM" for "Windows Imaging," is a file-based disk image format introduced in Windows Vista, the OS flop that debuted in 2007. Work on WIM, however, took place during the long -- and oft delayed -- development of "Longhorn," the code name for the project that was originally to produce an operating system in 2004.