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==== Structure of segment descriptor entry ==== <div> {| class="infobox" style="text-align:center" |- |style="text-align:center" |''80286 Segment descriptor'' |- | {| |style="width:15px;text-align:center"|<sup>3</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>0</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>9</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>8</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>7</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>6</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>5</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>4</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>2</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>0</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>9</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>8</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>7</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>6</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>5</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>4</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>2</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>0</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>9</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>8</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>7</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>6</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>5</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>4</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>2</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>0</sub> |- |colspan="16" style="background:silver;text-align:center"|Base[0..15] |colspan="16" style="background:silver;text-align:center"|Limit[0..15] |- |style="width:15px;text-align:center"|<sup>6</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>6</sup><sub>2</sub> |style="width:15px;text-align:center"|<sup>6</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>6</sup><sub>0</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>9</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>8</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>7</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>6</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>5</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>4</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>2</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>0</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>9</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>8</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>7</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>6</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>5</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>4</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>2</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>0</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>9</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>8</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>7</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>6</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>5</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>4</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>2</sub> |- |colspan="16" style="background:silver;text-align:center"|''Unused'' |colspan="1" style="background:silver;text-align:center"|P |colspan="2" style="background:silver;text-align:center"|DPL |colspan="1" style="background:silver;text-align:center"|S |colspan="1" style="background:silver;text-align:center"|X |colspan="1" style="background:silver;text-align:center"|C |colspan="1" style="background:silver;text-align:center"|R |colspan="1" style="background:silver;text-align:center"|A |colspan="8" style="background:silver;text-align:center"|Base[16..23] |} |} {| class="infobox" style="text-align:center" |- |style="text-align:center" |''80386 Segment descriptor'' |- | {| style="text-align:center" |style="width:15px;text-align:center"|<sup>3</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>0</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>9</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>8</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>7</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>6</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>5</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>4</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>2</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>2</sup><sub>0</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>9</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>8</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>7</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>6</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>5</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>4</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>2</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>1</sup><sub>0</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>9</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>8</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>7</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>6</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>5</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>4</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>2</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>0</sup><sub>0</sub> |- |colspan="16" style="background:silver;text-align:center"|Base[0..15] |colspan="16" style="background:silver;text-align:center"|Limit[0..15] |- |style="width:15px;text-align:center"|<sup>6</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>6</sup><sub>2</sub> |style="width:15px;text-align:center"|<sup>6</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>6</sup><sub>0</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>9</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>8</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>7</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>6</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>5</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>4</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>2</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>5</sup><sub>0</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>9</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>8</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>7</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>6</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>5</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>4</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>2</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>1</sub> |style="width:15px;text-align:center"|<sup>4</sup><sub>0</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>9</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>8</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>7</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>6</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>5</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>4</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>3</sub> |style="width:15px;text-align:center"|<sup>3</sup><sub>2</sub> |- |colspan="8" style="background:silver;text-align:center"|Base[24..31] |colspan="1" style="background:silver;text-align:center"|G |colspan="1" style="background:silver;text-align:center"|D |colspan="1" style="background:silver;text-align:center"|0 |colspan="1" style="background:silver;text-align:center"|''U'' |colspan="4" style="background:silver;text-align:center"|Limit[16..19] |colspan="1" style="background:silver;text-align:center"|P |colspan="2" style="background:silver;text-align:center"|DPL |colspan="1" style="background:silver;text-align:center"|S |colspan="1" style="background:silver;text-align:center"|X |colspan="1" style="background:silver;text-align:center"|C |colspan="1" style="background:silver;text-align:center"|R |colspan="1" style="background:silver;text-align:center"|A |colspan="8" style="background:silver;text-align:center"|Base[16..23] |} |} Where: *''A'' is the ''Accessed'' bit; *''R'' is the ''Readable'' bit; *''C'' (Bit 42) depends on ''X'':<ref name="OSDev GDT">{{cite web|url=https://wiki.osdev.org/Global_Descriptor_Table#Structure|title=Global Descriptor table - OSDev Wiki}}</ref> **if ''X'' = 1 then ''C'' is the ''Conforming'' bit, and determines which privilege levels can far-jump to this segment (without changing privilege level): ***if ''C'' = 0 then only code with the same privilege level as ''DPL'' may jump here; ***if ''C'' = 1 then code with the same or a lower privilege level relative to ''DPL'' may jump here. **if ''X'' = 0 then ''C'' is the ''direction'' bit: ***if ''C'' = 0 then the segment grows ''up''; ***if ''C'' = 1 then the segment grows ''down''. *''X'' is the ''Executable'' bit:<ref name="OSDev GDT"/> **if ''X'' = 1 then the segment is a code segment; **if ''X'' = 0 then the segment is a data segment. *''S'' is the ''Segment type'' bit, which should generally be cleared for system segments;<ref name="OSDev GDT"></ref> *''DPL'' is the ''Descriptor Privilege Level''; *''P'' is the ''Present'' bit; *''D'' is the ''Default operand size''; *''G'' is the ''Granularity'' bit; *Bit 52 of the 80386 descriptor is not used by the hardware. </div>
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