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Chapter 1. DOS and the Personal Computer > DOS and Random Access Memory

DOS and Random Access Memory

To understand the memory issues that surround DOS and your computer system, you first need to know a bit of history. When Intel designed the 8088 and 8086 processors on which the first generation of DOS computers (PCs and XTs) was based, Intel thought that no user would ever need more than one megabyte (1MB) of memory. Most of the computers then in use had only 64 kilobytes (64KB) of memory, so this speculation might have been reasonable at the time. The problem is that this speculation was wrong—very wrong.

Real Mode Versus Protected Mode

When Intel developed the 80286 processor, it created a new mode of operation that allowed the CPU to address memory of more than 1MB. Additionally, more than one program could run at the same time, with each program protected from the actions of other programs. This mode of operation was called protected mode.

To differentiate this new capability from the limited capabilities of the 8088 and 8086 processors, the term real mode was coined. Not until the release of the 80386 generation of processors did protected mode software begin to appear.



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