All these things must be decided upon and published so that both CPU and peripheral manufacturers know what to build so that their devices will talk to each other.

SCSI is an example of a standard. SCSI, pronounced "scuzzie," stands for noble concept: Small Computer Systems Interface. It specifies connector shapes, voltages, and a protocol. SCSI disk drives are disk drives whose controller adheres to the SCSI protocol and whose external connectors are the right shape for SCSI plugs. There are SCSI CD-ROMs, tape drives and printers.