What is the Global Descriptor Table memory type?

Question

What type of memory type is used for the Global Descriptor Table in an Intel Core 2 CPU?

Is it just EEPROM or does the CPU normally use another type of NVRAM?

Answer 1

The Global Descriptor Table is stored in normal memory (RAM), the CPU is told where it resides using the LGDT instruction. This happens in protected mode when the CPU is effectively a 16 bit processor and the instruction needs to be run in ring 0.

The CPU will retain references to the table (including in the segment registers) but it isn't physically stored on the CPU itself. And regardless, an x86 CPU does not have EEPROM.

You can find some good references here:

• http://www.jamesmolloy.co.uk/tutorial_html/4.-The%20GDT%20and%20IDT.html
• http://wiki.osdev.org/GDT_Tutorial#Telling_the_CPU_where_the_table_stands