The CBW instruction converts the signed byte in the AL register to a signed word in the AX register by extending the most significant bit of the AL register (the sign bit) into all of the bits of the AH register. The CWDE instruction converts the signed word in the AX register to a doubleword in the EAX register by extending the most significant bit of the AX register into the two most significant bytes of the EAX register. Note that the CWDE instruction is different from the CWD instruction. The CWD instruction uses the DX:AX register pair rather than the EAX register as a destination.