Some users have seen slower than expected disk input and output performance when running Windows NT guest operating systems. They see the problem in GSX Server virtual machines using IDE virtual disks on multiprocessor host computers. The I/O issue is especially noticeable when the virtual machine is booting.

You may increase performance by enabling DMA (direct memory access) on the virtual hard disk's IDE channel in the virtual machine.

If you have a virtual disk and a DVD/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 virtual machine settings editor (VM > Settings) to move the DVD/CD-ROM drive to the secondary IDE controller (channel 1) at IDE 1:0.

You can enable the DMA feature after you finish installing Windows NT. You must install Service Pack 3 or higher in the virtual machine to enable this option.

Once the virtual machine is running Windows NT, insert an SP3 or SP4 CD in the drive and run DMACHECK.EXE from the \SUPPORT\UTILS\I386 folder on the CD. Or download DMACHECK.EXE from the Microsoft Web site ( support.microsoft.com/support/kb/articles/Q191/7/74.ASP).

Click the Enabled option for the IDE controller and channel configured for the virtual disk. Typically, this is channel 0 only, unless you have the virtual machine configured with multiple virtual disks and no virtual DVD/CD-ROM drive.

As noted above, you should not enable DMA on an IDE channel with a virtual DVD/CD-ROM drive attached.