Segment descriptor

Descriptor as is known in the Intel x86 processor from 80286 ( introduced in 1982 ) is a structure describing a segment or a function in the memory.

A descriptor has a size of 8 bytes and contains the size, position, access rights and usage of a segment. In addition to the memory segments just described, there is also system segments that select for example an operating system function.

Descriptors are found exclusively in protected mode, the real mode, the segments have a constant size of 64 Kb, so they are not needed.

All of the descriptors are divided into three tables.

  • The GDT (Global Descriptor Table ) can hold up to 8192 descriptors and is available for all processes.
  • The LDT (Local Descriptor Table ) is a table, which is only available for a process. When a task switch and its contents are frequently changed.
  • The third table is the IDT ( Interrupt Descriptor Table ). It comprises 256 descriptors, each descriptor for which marks the start address of each interrupt.

Source / Web Link

  • Intel's documentation for system programmers (English)
  • Computer Architecture
Computer memory Task (computing)
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