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Extended memory is located above 1 MB, includes the high memory area, and ends at 16 MB on the Intel 286 and at 4 GB on the Intel 386DX and later.. In DOS memory management, extended memory refers to memory above the first megabyte (2 20 bytes) of address space in an IBM PC or compatible with an 80286 or later processor.
Several expanded-memory pages are bank-switched in the page frame, part of the upper memory area. In DOS memory management, expanded memory is a system of bank switching that provided additional memory to DOS programs beyond the limit of conventional memory (640 KiB). Expanded memory is an
Expanded memory managers such as Quarterdeck's QEMM product and Microsoft's EMM386 supported the expanded memory standard without requirement for special memory boards. On 386 and subsequent processors, memory managers like QEMM might move the bulk of the code for a driver or TSR into extended memory and replace it with a small fingerhold that ...
EMM386 is the expanded memory manager of Microsoft's MS-DOS, IBM's PC DOS, Digital Research's DR-DOS, and Datalight's ROM-DOS [1] which is used to create expanded memory using extended memory on Intel 80386 CPUs. There also is an EMM386.EXE available in FreeDOS. [2]
Prior to DOS extenders, if a user installed additional memory and wished to use it under DOS, they would first have to install and configure drivers to support either expanded memory specification (EMS) or extended memory specification (XMS) and run programs supporting one of these specifications.
QEMM provides access to the Upper Memory Area (UMA) and memory through the Expanded Memory Specification (EMS), Extended Memory Specification (XMS), Virtual Control Program Interface (VCPI) and DOS Protected Mode Interface (DPMI). Quickboot: It allows a form of warm reboot or local reboot to be performed without going through the BIOS.
Memory above the 1 MB limit was called extended memory. However the area between 640 KB and 1 MB was reserved for hardware addressing in IBM PC compatibles. DOS and other real mode programs, limited to 20-bit addresses, could only access this space through EMS emulation on the extended memory, or an EMS analog for extended memory.
In the mid- to later 1990s, while many games were still written for DOS, the 640 KB limit was eventually overcome by putting parts of the game's data above the first 1 MB of memory and using the code below 640 KB to access the extended memory using expanded memory (EMS) by making use of overlay technique.
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