Memory is cheap these days. Case in point: Newegg is currently selling an 8GB kit of Corsair's Vengeance DDR3-1600 DIMMs for less than $50. Despite the availability of cheap RAM, Microsoft is taking steps to reduce the memory usage of Windows 8. Redmond's efforts are detailed on the Building Windows 8 blog, which starts by comparing the new OS's memory usage with Windows 7. On a system with only a gig of RAM, Windows 7 idles at the desktop with a 404MB memory footprint. Windows 8 consumes just 281MB running on the same hardware.
Microsoft lists several changes that have lowered Win8's memory utilization, including a memory combining capacity that looks at the contents of system memory to see if any data is unecessarily duplicated. If it is, the OS will consolidate the identical data into a single copy. Should an application need to make changes to its share of that data, Windows 8 can spin off a new copy just for that app.
Services consume a chunk of system memory, and there will be fewer of them in Windows 8. In addition to removing a selection of services entirely, some previously classified as "always on" have been moved to manual startup and to a "start on demand" mode. This on-demand mode relies on trigger events to launch services, which will perform their duties before returning a dormant state.
Windows 8 will offer applications the ability to allocate "low priority" memory that the OS will target first if memory utilization climbs too high. Several low-level Windows components have also been tuned to reduce memory consumption. If you're using the Metro UI, Windows components associated with the standard desktop won't be loaded at all.
Interestingly, Microsoft says these optimizations are part of its efforts to deliver the full Windows experience on "SoC-based devices" the rest of the world calls tablets. The blog post specifically mentions leaving "lots of memory available for multiple concurrent apps," suggesting that true multitasking will feature prominently in Redmond's efforts to combat devices running Android and iOS.