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In real mode or V86 mode, the size of a segment can range from 1 byte up to 65,536 bytes (using 16-bit offsets). The 16-bit segment selector in the segment register is interpreted as the most significant 16 bits of a linear 20-bit address, called a segment address, of which the remaining four least significant bits are all zeros.
Far pointer. In a segmented architecture computer, a far pointer is a pointer to memory in a specific context, [1] such as a segment selector making it possible to point to addresses outside of the default segment. Comparison and arithmetic on far pointers is problematic: there can be several different segment-offset address pairs pointing to ...
The field SS0 contains the stack segment selector for CPL=0, and the field ESP0/RSP0 contains the new ESP/RSP value for CPL=0. When an interrupt happens in protected (32-bit) mode, the x86 CPU will look in the TSS for SS0 and ESP0 and load their values into SS and ESP respectively. This allows for the kernel to use a different stack than the ...
If clear, this is system segment, if 1, this is Code/Data segment. Type If bit 11 set, this is a code segment descriptor. If clear, this is a data/stack segment descriptor, which has "D" replaced by "B", "C" replaced by "E" and "R" replaced by "W". This is in fact a special case of the 2-bit type field, where the preceding bit 12 cleared as "0 ...
Memory segmentation is an operating system memory management technique of dividing a computer 's primary memory into segments or sections. In a computer system using segmentation, a reference to a memory location includes a value that identifies a segment and an offset (memory location) within that segment. Segments or sections are also used in ...
16-bit application. In the context of IBM PC compatible and Wintel platforms, a 16-bit application is any software written for MS-DOS, OS/2 1.x or early versions of Microsoft Windows which originally ran on the 16-bit Intel 8088 and Intel 80286 microprocessors. Such applications used a 20- bit or 24-bit segment or selector-offset address ...
Assuming a call gate has been set up already by the operating system kernel, code simply does a CALL FAR with the necessary segment selector (the offset field is ignored). ). The processor will perform a number of checks to make sure the entry is valid and the code was operating at sufficient privilege to use the g
Other variants include the fourteen-segment display which does not split the top or bottom horizontal segments, and the twenty-two-segment display [1] that allows lower-case characters with descenders. Often a character generator is used to translate 7-bit ASCII character codes to the 16 bits that indicate which of the 16 segments to turn on or ...