Many errors in a computer system are committed at the bit or byte level when information is either transmitted along communication lines from one computer to another or else within a computer from the memory to the microprocessor or from microprocessor to input/ output device. Such transfers are generally made over high-speed internal buses or sometimes over networks. The simplest technique to protect against such errors is the use of error-detecting and errorcorrecting codes. These codes are discussed in this chapter in this context. In Section 3.9, we see that error-correcting codes are also used in some versions of RAID memory storage devices.