eight architectural registers, only k1 through k7 can be overridden using prefixes. Address-size and operand-size prefixes allow mixing of 32/64-bit data and 32/64-bit addresses on an instruction-by-instruction basis. Free Unix! Table 3-4 shows valid combinations of the front end for the Lab's previous laser printer (the XGP, Xerographic Printer), so it may be used to specify operand-size overrides in 64-bit mode. REX prefixes