Essential Guide to Computer Data Storage: From Floppy to DVD, The

Serial Interface

If you send bits one at a time, you are using serial communication. If you send one extra bit for each 8 bits to make sure your data got there intact, it is called a parity bit (see Chapter 1). Bit parity can be odd or even. It is even if you assign 0 to the parity bit when the sum of 8 bits is an even number. You assign 1 to the parity bit when the sum is an odd number. The parity is called odd if the logic is reversed. After the byte has arrived, the system will sum 8 bits and check if the result matches the even-or-oddness predicted by the parity bit.

Two common connector types used for serial communication are the 9-pin connector DB9 and (less often) 25-pin DB25 connector, which are essentially the same. Figure 2-3 represents ...