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[ The PC Guide | Systems and Components Reference Guide | System Memory ]

Logical Memory Layout

"640K ought to be enough for anybody." -- Bill Gates, 1981.

Most computer buffs know this amusing quote well. However, many don't realize that it was actually IBM that made the majority of the logical memory layout decisions in the early PC that have given us so many of the wonderful design limitations that persist to this day. (This quote does illustrate how easily ten years can make anyone look silly who dares to predict how much of anything will be "enough" in the future. A recent one I heard was "nobody will ever need 1 GB of RAM in a desktop PC". I predict we'll be laughing at that one as well, and in less than five years. I remember the laughing--but not by me--at the notion of gigabyte hard drives.)

At any rate, early presumptions about memory size and usage have left an indelible mark on how PCs work with their system memory. This section takes a different look at memory, focusing on how it is allocated and used within the PC. The different ways that memory is used, and the important factors and system limitations in how memory is laid out, are explored to some degree. I don't go into too much detail here, as I am trying to keep to hardware aspects and much of this is quite software-related.

Next: Segment and Offset Memory Addressing

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