static/netbsd/man4/man4.x86/mem.4 4.html


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<table class="head">
  <tr>
    <td class="head-ltitle">MEM(4)</td>
    <td class="head-vol">Device Drivers Manual (x86)</td>
    <td class="head-rtitle">MEM(4)</td>
  </tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp"><code class="Nm">mem</code>, <code class="Nm">kmem</code> &#x2014;
    <span class="Nd">memory files</span></p>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp">The special file <code class="Nm">/dev/mem</code> is an interface
    to the physical memory of the computer. Byte offsets in this file are
    interpreted as physical memory addresses. Reading and writing this file is
    equivalent to reading and writing memory itself. Only offsets within the
    bounds of <code class="Nm">/dev/mem</code> are allowed.</p>
<p class="Pp">Kernel virtual memory is accessed through the interface
    <code class="Nm">/dev/kmem</code> in the same manner as
    <code class="Nm">/dev/mem</code>. Only kernel virtual addresses that are
    currently mapped to memory are allowed.</p>
<p class="Pp">On ISA the I/O memory space begins at physical address 0x000a0000
    and runs to 0x00100000.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="FILES"><a class="permalink" href="#FILES">FILES</a></h1>
<dl class="Bl-tag Bl-compact">
  <dt><span class="Pa">/dev/mem</span></dt>
  <dd style="width: auto;">&#x00A0;</dd>
  <dt><span class="Pa">/dev/kmem</span></dt>
  <dd style="width: auto;">&#x00A0;</dd>
</dl>
</section>
<section class="Sh">
<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1>
<p class="Pp">The <code class="Nm">mem</code>, <code class="Nm">kmem</code>
    files appeared in <span class="Ux">Version&#x00A0;6 AT&amp;T
  UNIX</span>.</p>
</section>
</div>
<table class="foot">
  <tr>
    <td class="foot-date">March 27, 2026</td>
    <td class="foot-os">NetBSD 10.1</td>
  </tr>
</table>