iAPX 286 Operating System Writers Guide 1983

USING HARDWARE PROTECTION FEATURESo -EXECUTABLESEGMENT~ -GATEFigure 2-8. Gated Interlevel Call and Return121960-9DESCRIPTOR TABLESA descriptor table is simply a segment containing an array of eight-byte entries, where each entry is adescriptor- Descriptors are stored in one of three classes of descriptor table:• Local descriptor table (LDT)• Global descriptor table (GDT)• Interrupt descriptor table (lDT)The descriptors in these tables define all the segments in the system. Each table has a variable upperlimit, so the size of the table need be no larger than required for the actual number of segments used.You define (he initial contents of descriptor tables through the Builder. An operating system for dynamicapplications may change .the contents of descriptor tables and may create and delete LDT's as taskscome and go. Correct management of descriptors is the heart of protection on the iAPX 286.2-12 121960-001