Windows NT uses 32-bit flat linear addressing for memory. NT views memory as a large uninterupted block of up to 4 Gigabytes (2 for applications, 2 for the operating system). DOS used 64K segments, so using a 2K memory chunk actually takes up 64K worth of memory. NT does away with segmentation.

As physical memory is used up, Windows NT can begin to use hard drive space as Virtual Memory. This uses a swap file called pagefile.sys. It is a hidden file normally located on the root of your boot partition. As memory is used, lower priority and non-recently used data is transferred to the hard disk. This swapping of memory is transparent to the application since NT controls the memory. Each application has a unique virtual address space composed of equal blocks called pages. Demand Paging is the moving of data between the file and the application as needed. Applications only can run when they are located in physical RAM.