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diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node29.html b/sag-0.6.1-www/Invisible/sag-0.6/node29.html new file mode 100644 index 0000000..6d65ed2 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node29.html @@ -0,0 +1,83 @@ +<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> +<!--Converted with LaTeX2HTML 96.1-h (September 30, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds --> +<HTML> +<HEAD> +<TITLE>Two kinds of devices</TITLE> +<META NAME="description" CONTENT="Two kinds of devices"> +<META NAME="keywords" CONTENT="sag"> +<META NAME="resource-type" CONTENT="document"> +<META NAME="distribution" CONTENT="global"> +<LINK REL=STYLESHEET HREF="sag.css"> +</HEAD> +<BODY LANG="EN" > + <A NAME="tex2html680" HREF="node30.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html678" HREF="node28.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html672" HREF="node28.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html682" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html683" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html681" HREF="node30.html">Hard disks</A> +<B>Up:</B> <A NAME="tex2html679" HREF="node28.html">Using Disks and Other </A> +<B> Previous:</B> <A NAME="tex2html673" HREF="node28.html">Using Disks and Other </A> +<BR> <P> +<H1><A NAME="SECTION00510000000000000000">Two kinds of devices</A></H1> +<P> + UNIX, and therefore Linux, recognizes two different + kinds of device: random-access block devices (such as disks), + and character devices (such as tapes and serial lines), + some of which may be serial, and some random-access. Each + supported device is represented in the filesystem as a + <b>device file</b>. When you read or write a device file, the + data comes from or goes to the device it represents. This way + no special programs (and no special application programming + methodology, such as catching interrupts or polling a serial + port) are necessary to access devices; for example, to send a + file to the printer, one could just say + <BLOCKQUOTE> <TT> +<code>$</code> <I>cat filename > /dev/lp1</I> <BR> +<code>$</code> + </TT></BLOCKQUOTE> + and the contents of the file are printed (the file must, of + course, be in a form that the printer understands). However, + since it is not a good idea to have several people cat their + files to the printer at the same time, one usually uses a special + program to send the files to be printed (usually <tt>lpr</tt><A NAME="1437"> </A>). + This program makes sure that only one file is being printed + at a time, and will automatically send files to the printer as + soon as it finishes with the previous file. Something similar + is needed for most devices. In fact, one seldom needs to worry + about device files at all. +<P> + Since devices show up as files in the filesystem (in the + <tt>/dev</tt><A NAME="1439"> </A> directory), it is easy + to see just what device files exist, using <tt>ls</tt><A NAME="1441"> </A> or + another suitable command. In the output of <tt>ls -l</tt><A NAME="1443"> </A>, the + first column contains the type of the file and its + permissions. For example, inspecting a serial device + gives on my system + <BLOCKQUOTE> <TT> +<code>$</code> <I>ls -l /dev/cua0</I> <BR> +<code>crw-rw-rw- 1 root uucp 5, 64 Nov 30 1993 /dev/cua0</code> <BR> +<code>$</code> + </TT></BLOCKQUOTE> + The first character in the first column, i.e., `<TT>c</TT>' in + <TT>crw-rw-rw-</TT> above, tells an informed user the type of the file, + in this case a character device. For + ordinary files, the first character is `<TT>-</TT>', for + directories it is `<TT>d</TT>', and for block devices `<TT>b</TT>'; + see the <tt>ls</tt><A NAME="1445"> </A> man page for further information. +<P> + Note that usually all device files exist even though the + device itself might be not be installed. So just because you + have a file <tt>/dev/sda</tt><A NAME="1447"> </A>, it doesn't mean that you really do + have an SCSI hard disk. + Having all the device files makes the installation programs + simpler, and makes it easier to add new hardware (there is no + need to find out the correct parameters for and create the device + files for the new device). +<P> +<HR><A NAME="tex2html680" HREF="node30.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html678" HREF="node28.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html672" HREF="node28.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html682" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html683" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html681" HREF="node30.html">Hard disks</A> +<B>Up:</B> <A NAME="tex2html679" HREF="node28.html">Using Disks and Other </A> +<B> Previous:</B> <A NAME="tex2html673" HREF="node28.html">Using Disks and Other </A> +<P><ADDRESS> +<I>Lars Wirzenius <BR> +Sat Nov 15 02:32:11 EET 1997</I> +</ADDRESS> +</BODY> +</HTML> |