Microsoft released a white paper at WinHEC about the system requirements of its next-generation Windows. Longhorn will requires PCs to have at least a modern CPU, 512MB memory and a graphics card with a Longhorn display driver model (LDDM).
Longhorn should run fine on PCs with 256MB RAM but Microsoft believes that 512MB and up will provide better multitasking performance.
Microsoft also stated that the majority of current processors will be fine for Longhorn and that dual-core processors will offer better multitasking performance.
By the end of this year Microsoft wants PC vendors to label their systems with a Longhorn Ready PC logo.