Intel IA-32 2.6.1 Loading and Storing System Registers

Vol. 3A 2-25
SYSTEM ARCHITECTURE OVERVIEW
2.6.1 Loading and Storing System Registers
The GDTR, LDTR, IDTR, and TR registers each have a load and store instruction for loading
data into and storing data from the register:
•LGDT (Load GDTR Register) — Loads the GDT base address and limit from memory
into the GDTR register.
•SGDT (Store GDTR Register) — Stores the GDT base address and limit from the GDTR
register into memory.
•LIDT (Load IDTR Register) — Loads the IDT base address and limit from memory into
the IDTR register.
•SIDT (Load IDTR Register — Stores the IDT base address and limit from the IDTR
register into memory.
•LLDT (Load LDT Register) — Loads the LDT segment selector and segment descriptor
from memory into the LDTR. (The segment selector operand can also be located in a
general-purpose register.)
MOV DRnLoad and store debug registers No Yes
INVD Invalidate cache, no writeback No Yes
WBINVD Invalidate cache, with writeback No Yes
INVLPG Invalidate TLB entry No Yes
HLT Halt Processor No Yes
LOCK (Prefix) Bus Lock Yes No
RSM Return from system management mode No Yes
RDMSR3Read Model-Specific Registers No Yes
WRMSR3Write Model-Specific Registers No Yes
RDPMC4Read Performance-Monitoring Counter Yes Yes2
RDTSC3Read Time-Stamp Counter Yes Yes2
NOTES:
1. Useful to application programs running at a CPL of 1 or 2.
2. The TSD and PCE flags in control register CR4 control access to these instructions by application
programs running at a CPL of 3.
3. These instructions were introduced into the IA-32 Architecture with the Pentium processor.
4. This instruction was introduced into the IA-32 Architecture with the Pentium Pro processor and the
Pentiumprocessor with MMX technology.
5. This instruction is not supported in 64-bit mode.
Table 2-2. Summary of System Instructions (Contd.)
Instruction Description Useful to Application? Protected from Application?