DOS 1.x (1981) had no explicit memory management support. It was designed to run primarily on machines with 64K RAM or less, or not too much more (the original PC could not have more than 64K RAM on the system board, although RAM expansion boards did exist). A COM program could easily access (almost) 64K memory when loaded, and many programs didn’t rely on even having that much. In fact the early PCs often only had 64K or 48K RAM installed. But the times were rapidly changing.
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