static/netbsd/man4/man4.vax/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 (vax)</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>,
    <code class="Nm">kUmem</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">The file <code class="Nm">/dev/kUmem</code> also refers to kernel
    virtual memory, but may be used to access areas mapped to UNIBUS address
    space and other I/O areas. It forces all accesses to use word (short
    integer) accesses.</p>
<p class="Pp">On the VAX-11/780, the I/O space base address is 20000000(16); on
    an 11/750 the I/O space addresses are of the form fxxxxx(16). On all VAX'en
    the per-process data size for the current process is
    <code class="Dv">UPAGES</code> long and ends at the virtual address
    80000000(16).</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>
  <dt><span class="Pa">/dev/kUmem</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>.
    The file <code class="Nm">kUmem</code> appeared in
    <span class="Ux">3.0BSD</span>.</p>
</section>
</div>
<table class="foot">
  <tr>
    <td class="foot-date">June 5, 1993</td>
    <td class="foot-os">NetBSD 10.1</td>
  </tr>
</table>