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			<title>Macintosh IIfx: DMA Access Support</title><body class="ac-gn-current-support">
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<h1 id="main-title">Macintosh IIfx: DMA Access Support</h1>
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<div id="intro-container"><div class="truncate"><div class="attr SYMPTOMS"><div class="attr TOPIC"><FONT SIZE=4> </FONT><BR>
<FONT SIZE=4> <BR>
Is DMA access supported to or from NuBus memory space on the Macintosh<BR>
IIfx?<BR>
 <BR>
Which drives will benefit from DMA on the Macintosh IIfx?  Is it only<BR>
internal drives?  Also, is it the same for both the A/UX and Macintosh OS?<BR>
 <BR>
</FONT></div></div> <!--  attr Symptom  --></div> <!--  truncate --></div> <!--  intro-container --><div class="clear"> </div>
 </div>   <!-- abstract end -->
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  <div class="attr SUMMARY">
DMA access is supported to and from main memory -- but not to or from<BR>
NuBus memory space.  (The only way to access NuBus memory is through the<BR>
NuBus controller chip, which is controlled by the 68030 CPU.  This makes<BR>
it impossible to do SCSI DMA involving NuBus memory on the Macintosh<BR>
IIfx.)<BR>
 <BR>
Currently, only A/UX 2.0 supports the SCSI DMA capabilities of the<BR>
Macintosh IIfx.  SCSI DMA is possible on all SCSI devices, not just the<BR>
internal SCSI device.  The internal and external SCSI connectors support<BR>
the same signals.<BR>
 <BR>
When running A/UX 2.0 on a Macintosh IIfx, any SCSI device (internal and<BR>
external) will benefit from the SCSI DMA capabilities of the Macintosh<BR>
IIfx.<BR>
<BR>
<BR></div>
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<div class="mod-date">Published Date: Feb 18, 2012</div>
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