LIM Expanded Memory Specification V4: Glossary

The following terms are used frequently in this specification:

Allocate	To reserve a specified amount of expanded memory pages.
Application	Program An application program is the program you write and your customer uses. Some categories of application software are word processors, database managers, spreadsheet managers, and project managers.
Conventional Memory	The memory between 0 and 640K bytes, address range 00000h thru 9FFFFh.
Deallocate	To return previously allocated expanded memory to the memory manager.
EMM	See Expanded Memory Manager.
Expanded Memory	Expanded memory is memory outside DOS's 640K-byte limit (usually in the range of C0000h through EFFFFH).
Expanded Memory	Manager (EMM) A device driver that controls the interface between DOS application programs and expanded memory.
Extended Memory	The 15M-byte address range between 100000h thru FFFFFFh available on an 80286 processor when it is operating in protected virtual address mode.
Handle	A value that the EMM assigns and uses to identify a block of memory requested by an application program. All allocated logical pages are associated with a particular handle.
Logical Page	The EMM allocates expanded memory in units (typically 16K-bytes) called logical pages.
Mappable Segment	A 16K-byte region of memory which can have a logical page mapped at it.
Map Registers	The set of registers containing the current mapping context of the EMM hardware.
Mapping	The process of making a logical page of memory appear at a physical page.
Mapping Context	The contents of the mapping registers at a specific instant. This context represents a map state.
Page Frame	A collection of 16K-byte contiguous physical pages from which an application program accesses expanded memory.
Page Frame	Base Address A page frame base address is the location (in segment format) of the first byte of the page frame.
Physical Page	A physical page is the range of memory addresses occupied by a single 16K-byte page.
Raw Page	The smallest unit of mappable memory that an expanded memory board can supply.
Resident Application Program	A resident application program is loaded by DOS, executes, and remains resident in the system after it returns control to DOS. This type of program occupies memory and is usually invoked by the operating system, an application program, or the hardware. Some examples of resident application programs are RAM disks, print spoolers, and "pop-up" desktop programs.
Status Code	A code that an EMM function returns which indicates something about the result of running the function. Some status codes indicate whether the function worked correctly and others may tell you something about he expanded memory hardware or software.
Transient Application	A transient application program is loaded Program by DOS, executes, and doesn't remain in the system after it returns control to DOS. After a transient application program returns control to DOS, the memory it used is available for other programs.
Unmap	To make a logical page inaccessible for reading or writing.

LIM Expanded Memory Specification V4 Contents

• Chapter 1: Introduction
• Chapter 2: Writing Programs that use Expanded Memory
• Chapter 3: EMM Function Reference
• Appendix A
• Appendix B
• Appendix C
• Appendix D
• Glossary (this page)

See Also

• Lo-tech 2MB EMS Board