1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>Chapter&#160;1.&#160;Introduction</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="SCSI Interfaces Guide"><link rel="up" href="index.html" title="SCSI Interfaces Guide"><link rel="prev" href="index.html" title="SCSI Interfaces Guide"><link rel="next" href="subsystem_design.html" title="Design of the Linux SCSI subsystem"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter&#160;1.&#160;Introduction</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="index.html">Prev</a>&#160;</td><th width="60%" align="center">&#160;</th><td width="20%" align="right">&#160;<a accesskey="n" href="subsystem_design.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="intro"></a>Chapter&#160;1.&#160;Introduction</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="sect1"><a href="intro.html#protocol_vs_bus">Protocol vs bus</a></span></dt><dt><span class="sect1"><a href="subsystem_design.html">Design of the Linux SCSI subsystem</a></span></dt></dl></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="protocol_vs_bus"></a>Protocol vs bus</h2></div></div></div><p>
2        Once upon a time, the Small Computer Systems Interface defined both
3        a parallel I/O bus and a data protocol to connect a wide variety of
4        peripherals (disk drives, tape drives, modems, printers, scanners,
5        optical drives, test equipment, and medical devices) to a host
6        computer.
7      </p><p>
8        Although the old parallel (fast/wide/ultra) SCSI bus has largely
9        fallen out of use, the SCSI command set is more widely used than ever
10        to communicate with devices over a number of different busses.
11      </p><p>
12        The <a class="ulink" href="http://www.t10.org/scsi-3.htm" target="_top">SCSI protocol</a>
13        is a big-endian peer-to-peer packet based protocol.  SCSI commands
14        are 6, 10, 12, or 16 bytes long, often followed by an associated data
15        payload.
16      </p><p>
17        SCSI commands can be transported over just about any kind of bus, and
18        are the default protocol for storage devices attached to USB, SATA,
19        SAS, Fibre Channel, FireWire, and ATAPI devices.  SCSI packets are
20        also commonly exchanged over Infiniband,
21        <a class="ulink" href="http://i2o.shadowconnect.com/faq.php" target="_top">I20</a>, TCP/IP
22        (<a class="ulink" href="http://en.wikipedia.org/wiki/ISCSI" target="_top">iSCSI</a>), even
23        <a class="ulink" href="http://cyberelk.net/tim/parport/parscsi.html" target="_top">Parallel
24        ports</a>.
25      </p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="index.html">Prev</a>&#160;</td><td width="20%" align="center">&#160;</td><td width="40%" align="right">&#160;<a accesskey="n" href="subsystem_design.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">SCSI Interfaces Guide&#160;</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">&#160;Design of the Linux SCSI subsystem</td></tr></table></div></body></html>
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