Descriptor Flags

Bit 55

Granularity: (G) 0=limit is in bytes, 1=limit is in 4K pages
Bit 54
Default address and operand (D/B) size: 0=16 bit, 1=32 bit

Note:

In code segment this bit (called the D bit) governs the default address and operand size.

In a data segment this bit is ignored.

In a stack segment this bit (called the B bit) determines whether SP (B=0) or ESP (B=1) is used by instructions that implicitly reference the stack, for example PUSH, POP, CALL and RET.

Bit 53
Reserved, must be zero.
Bit 52
Unused by hardware, used by OS/2 to indicate UVirt
Bit 47
Present: (P) 1=segment is present, 0=segment is not present
Bits 46 & 45
Privilege Level: 00=most, 11=least
Bit 44
Segment type: 0=system segment, 1=application segment
Bit 40
Accessed: (A) 0=not accessed, 1=accessed

Note: If application segment, ( Bit 44 = 1 ), used to store program code and data.

Bit 43=0 is Data Segment

Bit 42: Expansion: 0=Expand Up, 1=Expand Down

Bit 41: Writeable: 0=Read Only, 1=Read/Write

Bit 43=1 is Code Segment

Bit 42: Conforming: 0=Non-conforming, 1=Conforming

Bit 41: Readable: 0=Execute Only, 1=Read/Execute

Note: If system segment, ( Bit 44 = 0 )

Bits 39-42

Type of segment
00
RESERVED
01
Available 286 TSS ( 16-bit )
02
LDT
03
Busy 286 TSS ( 16-bit )
04
286 Call Gate ( 16-bit ) ( Parm Count is words )
05
Task Gate
06
286 Interrupt Gate ( 16-bit )
07
286 Trap Gate ( 16-bit )
08
RESERVED
09
Available 386 TSS ( 32-bit )
10
RESERVED
11
Busy 386 TSS ( 32-bit )
12
386 Call Gate ( 32-bit ) ( Parm count is doublewords )
13
RESERVED
14
386 Interrupt Gate (32-bit )
15
386 Task Gate ( 32-bit )

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