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The Unabridged Pentium 4 IA32 Processor Genealogy by Bob Colwell, Tom Shanley

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DOS Task's Memory Usage

1st MB Is DOS Memory

Each DOS task believes that it resides within and interacts with other programs residing within the first megabyte of memory space (the linear address range from 00000000h through 000FFFFFh; see Figure 15-2 on page 335).

Figure 15-2. DOS Task's Perception of the 1st MB of Memory Space

Paging Provides Each DOS Task with Its Own Copy of the 1st MB

If multiple DOS tasks are being run under a multitasking OS, each of them, when active, performs memory reads and writes within the first megabyte of linear memory space. The currently executing DOS task can easily alter the contents of memory locations that ...

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