Problem—Running Two (or more) DOS Programs
Application programs designed for the DOS environment are written using 8088 code and only access information in the first 1MB of memory space (i.e., from 00000000h through 000FFFFFh). Furthermore, each DOS application believes itself to be the only program executing and, as long as it doesn't mangle the OS (which also resides in the first 1MB area), it can access any location within the first 1MB of memory space.
If a multitasking OS were to load two or more DOS application programs into the first 1MB of memory, the second one loaded would almost certainly overwrite a portion of the first one (thereby rendering it useless). Even if they occupied mutually-exclusive areas of the first 1MB (highly unlikely), ...
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