Intel x86 Opcode Reference?

Question

What is a relatively quick and easy method of looking up what an arbitrary opcode means (say, 0xC8) in x86?

The Intel Software Developer\'s manual

Answer 1

Another way, using a debugger (gdb, windbg, ollydbg, ...) or disassembler (IDA), and then, set byte sequences in writable memory region. Finally, disassembly at the starting address of that byte sequences.
It's seam complicated, but useful in some situations when you cracking/reversing.