<chapter>
<title>Use of the System Disk</title>
<para>
Disk-based OS-9 systems use a system disk to load many parts of
the operating system during the system startup and to provide files
frequently used during normal system operations. Therefore, the
system disk is generally kept in disk drive zero (&quot;/D0&quot;) when the
system is running.
</para>
<para>
Two files used during the system startup operation, &quot;OS9Boot&quot; and
&quot;startup&quot; <emphasis>must</emphasis>
reside in the system disk's root directory. Other
files are organized into three directories: CMDS (commands), DEFS
(system-wide definitions), and SYS (other system files). Other files
and directories created by the system manager and/or users may also
reside on the system disk. These frequently include each user s
initial data directory.
</para>

<section>
<title>The OS9BOOT File</title>

<para>
The file called &quot;OS9Boot&quot; loaded into RAM memory by the
&quot;bootstrap&quot; routine located in the OS-9 firmware. It includes file
managers, device drivers and descriptors, and any other modules
which are permanently resident in memory. A typical Microware OS-9
distribution disk's &quot;OS9Boot&quot; file contains the following modules:
</para>
<informaltable frame="none">
<tgroup cols="2">
<colspec colwidth="1.5in"/>
<colspec colwidth="3.5in"/>
<tbody>
  <row>
    <entry>IOMAN</entry>
    <entry>OS-9 Input/Output Manager</entry>
  </row>
  <row>
    <entry>RBF</entry>
    <entry>Random Block (disk) File Manager</entry>
  </row>
  <row>
    <entry>SCF</entry>
    <entry>Sequential Character (terminal) File Manager</entry>
  </row>
  <row>
    <entry>Pipeman</entry>
    <entry>Pipeline File Manager</entry>
  </row>
  <row>
    <entry>Piper</entry>
    <entry>Pipeline Driver</entry>
  </row>
  <row>
    <entry>Pipe</entry>
    <entry>Pipeline Device Descriptor</entry>
  </row>
  <row>
    <entry>KBDVID</entry>
    <entry>Keyboard/video/Graphics Device Driver</entry>
  </row>
  <row>
    <entry>PRINTER</entry>
    <entry>Printer Device Driver</entry>
  </row>
  <row>
    <entry>DDISK</entry>
    <entry>Disk Driver</entry>
  </row>
  <row>
    <entry>D0, D1</entry>
    <entry>Disk Device Descriptor</entry>
  </row>
  <row>
    <entry>TERM</entry>
    <entry>Terminal Device Descriptor</entry>
  </row>
  <row>
    <entry>P</entry>
    <entry>Printer Device Descriptor</entry>
  </row>
  <row>
    <entry>CLOCK</entry>
    <entry>Real-Time Clock Module</entry>
  </row>
  <row>
    <entry>SYSGO</entry>
    <entry>System Startup Process</entry>
  </row>
</tbody>
</tgroup>
</informaltable>

<para>
Users may create new bootstrap files which may include additional
modules (see &quot;OS9Gen&quot; command). Any module loaded as part of the
bootstrap cannot be unlinked and is stored in memory with a minimum
of fragmentation. It may be advantageous to include in the OS9Boot
file any module used constantly during normal system operation.
This can be done with the OS9GEN command.
</para>
</section>

<section>
<title>The SYS Directory</title>

<para>
The directory &quot;/d0/SYS&quot; contains two important files:
</para>
<informaltable frame="none">
<tgroup cols="2">
<colspec colwidth="1in"/>
<colspec colwidth="4in"/>
<tbody>
  <row>
<entry>password</entry>
<entry>the system password file (see &quot;login&quot; command)</entry>
  </row>
  <row>
<entry>errmsg</entry>
<entry>the error message file (see 4.7)</entry>
  </row>
</tbody>
</tgroup>
</informaltable>
<para>
These files (and the SYS directory itself) are not absolutely
required to boot OS-9, they are needed if &quot;login&quot;, &quot;tsmon&quot;, or
&quot;printerr&quot; will be used. Users may add other system-wide files of
similar nature if desired.
</para>
</section>

<section>
<title>The Startup File</title>

<para>
The file &quot;/d0/startup&quot; is a shell procedure file (see 4.6) which
is automatically processed immediately after system startup. The
user may include in &quot;startup&quot; any legal shell command line. Often
this will include &quot;setime&quot; to start the system clock. If this file
is not present the system will still start correctly but the user
must run the SETIME command manually.
</para>
</section>

<section>
<title>The CMDS Directory</title>

<para>
The directory &quot;/d0/CMDS&quot; is the system-wide command object code
directory, which is normally shared by all users as their working
execution directory (see 3.7). If &quot;shell&quot; is not part of the
&quot;OS9Boot&quot; file, it must be present in this directory. The system
startup process &quot;sysgo&quot; makes CMDS the initial execution directory.
</para>
</section>

<section>
<title>The DEFS Directory</title>

<para>
The directory &quot;/d0/DEFS&quot; is a directory that contains assembly
language source code files which contain common system-wide symbolic
definitions, and are normally included in assembly language programs
by means of the OS-9 Assembler &quot;use&quot; directive. The presence and
use of this directory is optional, but highly recommended for any
system used for assembly language programs. The files commonly
contained in this directory are:
</para>
<informaltable frame="none">
<tgroup cols="2">
<colspec colwidth="1in"/>
<colspec colwidth="4in"/>
<tbody>
  <row>
<entry>OS9Defs</entry>
<entry>main system-wide definition file</entry>
  </row>
  <row>
<entry>RBFDefs</entry>
<entry>RBF file manager definition file</entry>
  </row>
  <row>
<entry>SCFDefs</entry>
<entry>SCF file manager definition file</entry>
  </row>
  <row>
<entry>Systype</entry>
<entry>System types definition file</entry>
  </row>
</tbody>
</tgroup>
</informaltable>

</section>

<section>
<title>Changing System Disks</title>

<para>
The system disk is not usually removed while the system is running, especially
on multiuser systems. If it is, the &quot;chx&quot; and
&quot;chd&quot; (if the working data directory was on the system disk)
commands should be executed to reset the working directory pointers
because the directories may be at different addresses on the new
disk, for example:
</para>

<screen>
chx /d0/cmds
chd /d0
</screen>

<para>
In general, it is unwise to remove a disk and replace it with
another if any paths are open to files resident on the disk. It is
<emphasis>dangerous</emphasis> to exchange <emphasis>any</emphasis>
disk if any files on it are open in WRITE or UPDATE modes.
</para>


</section>

<section>
<title>Making New System Disks</title>

<para>
To make a system disk, the following steps must be performed:

<orderedlist  numeration="arabic">
<listitem><para>
The new disk must be formatted.
</para></listitem>

<listitem><para>
The &quot;OS9Boot&quot; file must be created and linked by the &quot;OS9Gen&quot; or
&quot;Cobbler&quot; commands.
</para></listitem>

<listitem><para>
The &quot;startup&quot; file must be created or copied.
</para></listitem>

<listitem><para>
The CMDS and SYS directories and the files they contain must be
copied.
</para></listitem>
</orderedlist>

Steps 2 through 4 may be performed manually, or automatically by any
of the following methods:
<orderedlist  numeration="arabic">
<listitem><para>
By a shell procedure file created by the user.
</para></listitem>

<listitem><para>
By a shell procedure file generated by the &quot;dsave&quot; command
</para></listitem>

<listitem><para>
By the &quot;backup&quot; command
</para></listitem>
</orderedlist>
</para>
</section>
</chapter>