Descritors are describing System Segments, Memory Segments and Gates.
System Segments
Name
Bit
Full Name
Description
Limit
0..15
Limit 0..15
Memory range.
BAddr
16..39
Base Address 0..23
Physical address where the memory range begins.
Typ
40..43
Descriptor Type
Possible types :
0000b=0x0
unused (invalid Descriptor)
0001b=0x1
80286-TSS, 16 bit
0010b=0x2
LDT
0011b=0x3
activ 80286-TSS, 16 bit
1001=0x9
80386-TSS, 32 bit
1011=0xB
activ 80386-TSS, 32 bit
S
44
Storage Segment
= 0 for System Segments.
DPL
45,46
Descriptor Privilege Level
Specifies which Privileg Level a process minimum must have to use this Descriptor.
P
47
Present
defines if this Descriptor is "present" in memory. s. Paging .
Limit
48..51
Limit 16..19
high part of the Limit.
AVL
52
.
0
53
.
-
54
.
G
55
.
BAddr
56..63
Base Address 24..31
Higher part of the Base Address.
Memory Segments
Name
Bit
Full Name
Description
Limit
0..15
Limit 0..15
Memory range.
BAddr
16..39
Base Address 0..23
Physical address where the memory range begins.
A
40
WR
41
CE
42
EX
43
S
44
Storage Segment
= 1 for Memory Segments.
DPL
45,46
Descriptor Privilege Level
Specifies which Privileg Level a process minimum must have to use this Descriptor.
P
47
Present
defines if this Descriptor is "present" in memory. s. Paging .
Limit
48..51
Limit 16..19
high part of the Limit.
AVL
52
.
0
53
.
B
54
.
G
55
.
BAddr
56..63
Base Address 24..31
Higher part of the Base Address.
Gate Descriptor
Name
Bit
Full Name
Description
Offset
0..15
Offset 0..15
Lower part of the offset address (also known as pointer).
Selector
16..31
Selector
Selector that specifies the segment of the function to call.
DWC
32..35
Double Word Counter
.
0
36..39
-
Have to be 0.
Typ
40..43
Gate Type
Possible gate types :
S
44
Storage Segment
= 0 for interrupt gates.
DPL
45,46
Descriptor Privilege Level
Gate call protection. Specifies which Privileg Level the calling process minimum should have.
P
47
Present
can be set to 0 for Paging .
Offset
48..63
Offset 16..31
Higher part of the offset.