Alternatively called conventional memory, the 640 KB barrier is the PC compatible limit imposed by DOS mode that allows DOS programs to address a total of only 1 MB of memory. Because the system required 384 KB to be reserved, this left the lower 640 KB for DOS and other programs.

Memory terms

Bill Gates is often misquoted as saying “640 K ought to be enough for anybody.”

  • Computer memory diagram.
  • Memory (RAM) help and support.