NT allocates memory as a single block, and does not divide memory up into separate chunks, like DOS does. This type of architecture is called "linear" or "flat" addressing.

Each Process or Appliction has available up to 4gb of memory, which is comprised of both Physical Memory (RAM) and temporary storage on a Hard Disk.

Memory is allocated in pages, each of which is 4kb. The memory pages written to the hard drive, the virtual memory, are stored in the file called Pagefile.sys.

The memory allocation method used by NT is called demand paging. The Virtual Memory Manager handles all requests by applications to use memory. When the RAM is filled, the VMM then will write to the Pagefile.sys those areas of memory that sat in RAM the longest. If an application requests data that is stored in the Pagefile.sys, the VMM swaps that page from disk to RAM and, if necessary, writes a different page from RAM to Pagefile.sys.

An insufficient amount of RAM (physical memory) can seriously affect system performance. If too many processes try to access the RAM at the same time, the VMM will be swapping pages continually from the physical memory to disk and back. This is a relatively slow procedure compared to the speed of direct RAM access.

If this is a concern, use the Performance Monitor to look at the Memory object and count Pages/sec, Cache Faults, Page Faults, etc.

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