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37. Older OS and Addressing Modes Compared

The MS-DOS and Older Windows Operating Systems
Operating
System
System
Access
Available
Active
Processes
Addressable
Memory
Contents of Segment
Register
Word Length
MS-DOS and Windows real mode Direct to hardware and OS call One 1 megabyte Actual
address
16 bits
Windows 3.x virtual-86 mode Operating system call Multiple 1 megabyte Segment
selectors
16 bits
Windows 3.x protected mode Operating system call Multiple 16 megabytes Segment
selectors
16 bits
Windows NT 3.x Operating system call Multiple 512 megabytes Segment
selectors
32 bits

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