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<h2>3.9 How to configure your system for DJGPP</h2>

<p><em><strong>Q</strong>: How do I configure my system to get optimal performance under
DJGPP?</em>

<br><p>
<p><strong>A</strong>:  That depends on the amount of RAM you have installed in your
machine.  Below are some guidelines to help you.

<ol type=a start=1>
</p><li>If you have 2 MBytes or less RAM installed:

<ul>
<li>Don't use <strong>any</strong> memory manager. 
<li>Use of CWSDPMI as your DPMI host is highly recommended. 
<li>Remove any TSR and device drivers you don't absolutely need (like
<code>SETVER.EXE</code>, <code>HIMEM.SYS</code> etc.) from your <code>CONFIG.SYS</code>
and <code>AUTOEXEC.BAT.</code>
<li>Do <strong>not</strong> install disk cache or RAM disk; point your <code>TMPDIR</code>
environment variable to a directory on your hard disk.  Put a
sufficiently large <code>BUFFERS=</code> statement into your <code>CONFIG.SYS</code>
(I recommend setting <code>BUFFERS=40,8</code>) to make DOS file operations
faster<a rel=footnote href="faq25.html"><sup>8</sup></a>. 
<li>If you use CWSDPMI as your DPMI host, get the <code>CWSPARAM</code> program
(from the <code>csdpmi4b.zip</code> archive) and set the
"Minimum application memory desired before 640K paging" parameter to
512K or larger.  Depending on how much memory you actually have, you
might need to further fine-tune this parameter.  This parameter defines
the lowest amount of extended memory CWSDPMI will use; if your system
doesn't have that much free extended RAM, CWSDPMI will use conventional
memory instead, where usually there should be around 600K of free RAM. 
<li>If you run under Windows, be sure to set the maximum amount of extended
memory on your PIF file for the DOS box to a reasonable value. 
</ul>

<p>With this configuration, GCC will run out of free physical RAM and start
paging when compiling almost any C program and all C<tt>++</tt> programs.  If
you are serious about DJGPP development, you need to buy more RAM
<strong>urgently</strong>.

</p><li>If you have 2-4 MBytes of RAM installed:

<ul>
<li>Don't use <strong>any</strong> memory manager.

<li>Remove any TSR and device driver you don't absolutely need (like
<code>SETVER.EXE</code>, <code>HIMEM.SYS</code>) from your <code>CONFIG.SYS</code> and
<code>AUTOEXEC.BAT.</code>

<li>Get a disk cache which works from conventional memory and configure it to
256K size at most, or don't use a cache at all.

<li>Do <strong>not</strong> install a RAM disk; point your <code>TMPDIR</code> environment
variable to a directory on your hard disk.

<li>If you run under Windows, be sure to set the maximum amount of extended
memory on your PIF file for the DOS box to a reasonable value. 
</ul>

<p>With this configuration, GCC will still run out of free physical RAM and
start paging when compiling large C programs and most C<tt>++</tt> programs. 
Plan to buy more RAM as soon as you can.

</p><li>If you have 5-8 MBytes of RAM installed:

<ul>
<li>Use a memory manager such as <code>EMM386</code> or <code>QEMM386</code>.  Try using
the <code>FRAME=NONE</code> parameter of the memory manager.  This will
disable Expanded Memory (EMS) services as far as most programs are
concerned; if you must use DJGPP together with any program which needs
EMS, try to configure that program to use Extended Memory (XMS) instead.

<li>Load DOS, device drivers and TSRs <strong>HIGH</strong>.  This is done by using
the <code>DEVICEHIGH=</code> command (instead of <code>DEVICE=</code> in
<code>CONFIG.SYS</code>, and by using the <code>LOADHIGH</code> command in
<code>AUTOEXEC.BAT</code>.

<li>Give your disk cache 1 MByte of RAM.  Enable its delayed-write (a.k.a. 
write-back) feature.

<li>Do <strong>not</strong> install a RAM disk; point your <code>TMPDIR</code> environment
variable to a directory on your hard disk.

<li>If, after configuring your system as above, you still have more than 2.5
MBytes of free RAM left (4 MBytes, if you plan to program in C<tt>++</tt> a lot),
enlarge the disk cache size.

<li>If you run under Windows, be sure to set the maximum amount of extended
memory on your PIF file for the DOS box to a reasonable value. 
</ul>

<li>If you have more than 8 MBytes of RAM:

<ul>
<li>Use a memory manager to load DOS, TSRs and device drivers <strong>HIGH</strong>.

<li>Install at least a 2-MByte-large disk cache, configured to use the delayed-
write feature.  If you have plenty of RAM, you can give your cache as much
as 8 MBytes of memory.  Here's an example of a line to put into your
<code>AUTOEXEC.BAT</code> file that installs an 8-MByte cache for hard disks
<code>C:</code>, <code>D:</code>, and <code>F:</code>:

<pre>loadhigh c:\dos\smartdrv.exe c+ d+ f+ 8192
</pre>

<p>(The <code>+</code> character after the drive letter enables the delayed-write
(a.k.a. write-back) feature for that drive.)  Note that you do
<strong>not</strong> need, and should not install a disk cache if you intend to
use DJGPP programs from Windows 9X, because Windows includes its own
built-in disk cache (called <code>VCACHE</code>) that is loaded together with
the operating system.

</p><li>If you have more than 10 MBytes left, install a RAM disk with a size of at
least 1.5 MBytes and point your <code>TMPDIR</code> environment variable to it. 
If your RAM disk is less than 4 MBytes, GCC might run out of space there
for <em>very</em> large source files (e.g., cccp.c file from the GCC source
distribution), but this shouldn't happen unless the size of the source
file you are compiling approaches 1 MByte.  Note that software is
available that lets you install a RAM disk even on Windows 9X. 
(However, I'm told that Microsoft's own <code>RAMDRIVE.SYS</code> only
supports long file name on the RAM disk if its size is less than 9MB.)

<li>As a general rule of thumb, you should leave at least 8 MBytes of free
RAM after installing the disk cache and the RAM disk.  16MB free is even
better, especially if you need to run large programs like <small>RHIDE</small> or
Emacs, or to compile large source files. 
</ul>
</ol>

<p>Some people disable the delayed-write feature for safety reasons, to
avoid losing files due to system crashes.  If you are worried about this,
you can usually gain performance without sacrificing safety by enabling
delayed-write together with an option that causes the cache to flush the
write-behind data before the system returns to the DOS prompt.  For a
<code>SmartDrv</code> disk cache, this is achieved by specifying <code>/N/F</code>
switches instead of <code>/X</code>.

<p>Using a memory manager, such as <code>EMM386</code> or <code>QEMM</code>, is not
required (DJGPP will run without it), but highly recommended, since it
has several advantages:

<ul>
<li>Memory managers provide an API for allocating extended memory called
VCPI (the <dfn>Virtual Control Program Interface</dfn>).  Using that API
allows CWSDPMI to allocate only as much extended memory as is needed,
leaving the rest for non-DJGPP programs, in case you invoke them from
DJGPP programs.  In contrast, without a memory manager, CWSDPMI will
allocate all of the available extended memory to itself, leaving none of
it to non-DJGPP programs.  This consideration is especially important if
you use some DJGPP program, like Bash or Emacs, as your primary system
interface.

<li>Without a memory manager, you cannot access UMBs (the <dfn>Upper Memory
Blocks</dfn>) which give you more DOS memory to work with.  In particular,
CWSDPMI will load itself into UMBs if they are available.

<li>Memory managers provide the VDS (<dfn>Virtual DMA Services</dfn>) API which
allows to write programs that use DMA in protected mode.

<li>Memory managers support the expanded (EMS) memory, which some older DOS
programs still use. 
</ul>

<p>If your memory manager is <code>EMM386</code>, I recommend to put the
<code>NOEMS NOVCPI</code> parameters on its command line.  This will allow you
to use UMBs and up to 128MB of physical memory (if you have that much
installed).  Without these parameters, many versions of <code>EMM386</code>
limit your physical memory to 32MB.

<p>It is generally not recommended to install DJGPP on a networked drive,
since this makes it slower, particularly when linking programs.  If you
do install DJGPP on a networked drive, you should consult your network
administrator to configure the network for maximum performance.  For
Novell networks, a good place to look for advice is the Novell FAQ
(search for a file called <code>nov-faq.htm</code>).

<p><hr>
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