Enabling IDE DMA on Windows-based Systems

Updated: December 4, 2001

Many people are familiar with the gains to be had from using IDE hard drives and CD-ROM drives in DMA mode; a typical machine today will use 40% of the CPU doing hard drive transfers in PIO mode and use only 25% of the CPU doing hard drive transfers in DMA mode, on the same hardware.

If it is known that there is DMA-capable IDE hardware in the system, an easy way to make sure the machine is set up to use DMA is to add two lines to the Mshdc.inf file using the OPK tools available to OEMs. The Mshdc.inf file must be changed before the system is set up (really before the IDE devices are enumerated and installed). If the system is already set up, Mshdc.inf can be modified and all IDE devices manually removed from Device Manager, and then re-detected and enumerated and installed, which will set them up in DMA mode.

In the Mshdc.inf file, add to the [ESDI_AddReg] section the two bold-faced lines shown in the following example. The first 3 lines (not bold) should already appear in the file.

[ESDI_AddReg]
HKR,,DriverDesc,,"ESDI Port Driver"
HKR,,DevLoader,,*IOS
HKR,,PortDriver,,ESDI_506.pdr
HKR,,IDEDMADrive0,3,01
HKR,,IDEDMADrive1,3,01

To check that DMA has been set up correctly, go to Device Manager and view devices by type. Click Disk Drives, select the disk drive in question, click Properties, and then click the Settings tab. In the Options section, there should be a DMA check box, and it should be checked if DMA is being used.

Important:

•	For Microsoft Windows 98, you just have to enable the driver, since the fix is already incorporated. In all cases, you must implement the INF entries described in this article.
•	This feature will not work on Windows 95 gold; it is a feature first introduced in Windows 95 OSR2.
•	If the system has UltraDMA/33 hardware and not just DMA, you should pick up QFE513, which fixes an error recovery problem.
•	If you have problems, please contact your Premier Technical Support at Microsoft. Or see http://support.microsoft.com/default.aspx?PR=ddk.

Top of page