reading the system clock value?

Is there a virtual/system clock runnin开发者_JS百科g independently when a computer is booted?

How can we read that value?

Use the RDTSC x86 instruction, it reads the clocks since the system-start.

Edit: On x86-64 targets the use of inline assembly is not possible anymore, use either intrinics or a external linked object file which was generated by an assembler. Do not forget to flush the processor pipeline before using this instruction.