The 8088 processors used in the IBM PCs, XTs and compatibles only have the capability of directly addressing 1MB of RAM. This limit was greatly increased when the 80286 was built with the ability to address 16MB of RAM. The memory above the first MB in an 80286 and 80386 computer is referred to as "extended" memory. Unfortunately, the 640K limit still exists for most MS-DOS programs. A few programs have the capability of using extended memory; however, a more common option is to use a memory manager or device driver to allow the extended memory to emulate "expanded" memory. (7/96)
Memory above the 1MB mark in an 80286/386 machine. Used in OS/2 and Windows/386 environments. Not much use in a DOS environment. Obsolete.
Memory above 1Mb in 80286 and higher computers. Can be used for RAM disks, disk caches, or Microsoft Windows, but requires the processor to operate in a special mode (protected mode or virtual real mode). With a special driver, you can use extended memory to create expanded memory. See also memory, RAM, ROM