Block-oriented protocols (also known as block-level protocols) read and write individual fixed-length blocks of data. SCSI is a block-level I/O protocol for writing and reading data blocks to and from a storage device. Data transfer is also governed by standards. SCSI is an American National Standards Institute (ANSI) standard that is one of the leading I/O buses in the computer industry. The SCSI bus is a parallel bus, which comes in a number of variants, as shown in Table 6-2. The first version of the SCSI standard was released in 1986. Since then, SCSI has been continuously developed.