What the heck is RDTSC?

[n00b!]

I searched for it in opcodes.chm and I used Google but I did not find out what "RDTSC" does...
OllyDbg says it's a correct mnemonic for a working machine opcode...

Thanks!


EDIT: Ah, was too lazy to read...

http://en.wikipedia.org/wiki/Time_Stamp_Counter
"It counts the number of ticks since reset, and is only accessible through the RDTSC instruction. This instruction returns the TSC in EDX:EAX"

[donkey]

ReaD Time Stamp Clock

moves the count of the time stamp clock (in ticks) into the EDX:EAX register pair. The time stamp clock keeps track of the number of ticks since the machine was turned on or reset.

[ecube]

whats its downsides, why not use that instead of gettickcount?

[BlackVortex]

whats its downsides, why not use that instead of gettickcount?

GetTickCount is extremely inaccurate. RDTSC is inconsistent between different cpus though.

[MichaelW]

The problem with GetTickCount is not its accuracy - because it's probably using the same frequency reference as the other counters in the system - the problem is its relatively low resolution, 10ms by default, or 1ms at best. The Time Stamp Counter (TSC) is the highest resolution counter available, with a period that can be in the sub-nanosecond range. For a processor with a variable clock speed the TSC is not very useful as a time base (e.g. as the basis for a timer or a short programmable delay), but its usefulness for "timing" code (or whatever) in clock cycles is unaffected.

[Rainstorm]

Thanks for the explanation, this answered a few questions i had in my mind too.