Problem
Some users have seen slower than expected disk input/output performance when
running Windows NT guest operating systems in a virtual machine using IDE
virtual disks on a multiprocessor host computer. The I/O issue is especially
noticeable when the virtual machine is booting.
Resolution
You may increase performance by enabling DMA (direct memory access) on the
virtual hard disk's IDE channel in the virtual machine.
Note: You should not enable DMA on the IDE channel to which you have
attached your virtual CD-ROM drive. In most cases, the virtual hard disk is
attached to IDE channel 0 and the virtual CD-ROM drive is attached to IDE
channel 1, so this is not an issue.
If you have a virtual disk and a CD-ROM attached as master and slave to the
primary IDE controller (channel 0) and you want to enable DMA, power off the
virtual machine and use the Configuration Editor to move the CD-ROM to the
secondary IDE controller (channel 1) at IDE 1:0.
The DMA feature can be enabled after Windows NT has been successfully
installed. Service Pack 3 or later must be installed in the virtual machine
to enable this option.
Once the virtual machine is running Windows NT, insert the SP3 or SP4 CD in
the drive, run DMACHECK.EXE from the \SUPPORT\UTILS\I386
directory on the CD. Or download DMACHECK.EXE from the Microsoft
Web site (http://support.microsoft.com/support/kb/articles/Q191/7/74.ASP).
Click the Enabled option for the IDE controller/channel that is configured
with the virtual disk. Typically, this will be channel 0 only, unless you
have the virtual machine configured with multiple virtual disks and no
virtual CD-ROM drive. As noted above, you should not enable DMA on an IDE
channel with a virtual CD-ROM drive attached.