Memory Management in PCs: The Eighteen Most Misunderstood Acronyms

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Specific jargon and abbreviations provide a means of simplification in communicating complex ideas among members of any profession. While a convenience to experienced professionals, jargon can form a language barrier that is a formidable obstacle to newcomers. This is perhaps as much the case for accounting and information systems (AIS) professionals as it is for doctors, Lawyers, or engineers. Apart from all the accounting, auditing, legal, and client-industry specific jargon that modern-day accountants must be conversant with, there is also the plethora of computer and electronic engineering terminology that must be learned.

Some of the most confusing computer terms relate to memory-management in personal computers. For example, similar terms in personal computers. For example, similar terms are often used such as, expanded and extended, or high and upper memory. These terms refer to different concepts, in spite of the similarity of words. The acronyms commonly used for these concepts sometimes reflect the wrong characters as a means of distinguishment. For example, the difference between expanded memory and extended memory should be highlighted by emphasizing the "PA" of exPAnded or "TE" of exTEnded--otherwise the words are identical. Yet, the literature uses "El" (in EMS--expanded memory specification) or "XM" (in XM--extended memory specification) to describe the to terms, respectively. The letters EM and XM are both found in both terms, and do not distinguish the two terms at all for an uninitiated newcomer.

Random Access Memory (R1) in a PC starts with the first megabyte (1024k) of RAM divided into lower (conventional) memory, which is the base 640k found in most machines, while the remaining 384k of the first megabyte is known as High Memory. The High Memory consists of upper memory blocks (UMBs) where certain programs can be stored by using suitable memory management software. To add to user confusion, the first 64k of exTEnded memory (RAM just above the first megabyte) is known as the High Memory Area (HMA). It is the next area above the first 1024k, and has nothing to do with the 384k High Memory previously described. Needlessly confusing? Memory addressed above the first 1024k is exTEnded memory.

For the most part, exTEnded memo can be used only for RAM disks, disk caching software, and certain Windows uses, unless it is converted to exPAnded memory. ExPAnded memory is any mapped-into the memory that can be base 640k; that is, DOS can be tricked into accepting exPAnded memory as if it were conventional 640k memory. ExTEnded memory can be converted to exPAnded memory by using memory management software. ExPAnded memory has more versatile uses memory, such as being usable by spreadsheet programs for loading large files into RAM all at once.

The industry-standard specifications for exPAnded memory started with the Lotus-Intel-Microsoft Expanded Memory Specification (LIM-EMS), then the Enhanced Expanded Memory Specification (EEMS) endorsed by AST Research, Quadram, and Ashton-Tate. The EEMS increased the amount of accessible exPAnded memory beyond the early 64k amount provided under LIM-EMS. Current EMS standards have unified and elaborated upon both of these two early approaches. …