<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML ><HEAD ><TITLE >Disk driver (sd)</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="HOME" TITLE="The Linux 2.4 SCSI subsystem HOWTO" HREF="index.html"><LINK REL="UP" TITLE="Upper level drivers" HREF="ulevel.html"><LINK REL="PREVIOUS" TITLE="Upper level drivers" HREF="ulevel.html"><LINK REL="NEXT" TITLE="CDROM driver (sr or scd)" HREF="sr.html"></HEAD ><BODY CLASS="sect1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >The Linux 2.4 SCSI subsystem HOWTO</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="ulevel.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 9. Upper level drivers</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="sr.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="sect1" ><H1 CLASS="sect1" ><A NAME="sd" ></A >9.1. Disk driver (sd)</H1 ><P > Two types of SCSI devices are accessible via the sd driver: <P ></P ><UL ><LI ><P >"direct access" devices which are usually magnetic disks. [SCSI peripheral device code is 0]</P ></LI ><LI ><P >"Optical memory devices" which are often called MOD disks. [SCSI peripheral device code is 7]</P ></LI ></UL > The sd driver is a block device which means that it is closely associated with the block subsystem. It also supports the concept of partitions. [<B CLASS="command" >man sd</B > dates from 1992.] </P ><P > The sd driver is capable of recognizing 128 disks when it is loaded at kernel boot time or later as a module. However, once it is loaded, it will only recognize a fixed number of additional disks. The number of additional disks that can be accommodated is set by the kernel configuration parameter CONFIG_SD_EXTRA_DEVS whose default value is 40. </P ><DIV CLASS="sect2" ><H2 CLASS="sect2" ><A NAME="sdbparams" ></A >9.1.1. sd boot parameters</H2 ><P > None. </P ></DIV ><DIV CLASS="sect2" ><H2 CLASS="sect2" ><A NAME="sdmparams" ></A >9.1.2. sd module parameters</H2 ><P > The sd driver takes no parameters when loaded as a module. Note that its module name is <TT CLASS="filename" >sd_mod.o</TT >. </P ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="ulevel.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="sr.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Upper level drivers</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ulevel.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >CDROM driver (sr or scd)</TD ></TR ></TABLE ></DIV ></BODY ></HTML >