While the SCSI interface is widely implemented on high-end hardware due to its
flexibility and high performance, its complexity does mean that some of its potential
performance is lost to overhead. In an effort to improve SCSI bus performance by reducing
overhead, the SPI-3 SCSI standard describes a new feature
that is generally called packetization or packetized SCSI.
Packetization is a technique whereby some of the phases that are involved in setting up
a command request and data transfer are combined. For example, under traditional SCSI
interfacing, several different types of information are sent over the bus separately:
commands, data, status messages and so on. With packetization, these are grouped together
into packets (also called information units) and sent as a single
entity. This reduces some of the wasted bus cycles normally sent on managing all the
individual transfers in regular SCSI.
Packetization is one of the five "optional" features of Ultra3 SCSI. It was not included as one of the required
features for hardware meeting the Ultra160 specification,
but is present in Ultra160+ devices. It may also be
part of the requirements for Ultra320 SCSI when that
specification is complete.
Next: SCSI Protocol Map
