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November 16, 1998

You can fix problems with Ultra DMA drives in Windows 95/98, NT

Last week, I described problems that some Windows users are having with so-called Ultra Direct Memory Access (UDMA) hard drives -- drives that can theoretically transfer files as fast as 33.3MBps, as opposed to 16.6MBps under the original IDE standard.

This week, I'll tell you how such symptoms can show up under Windows and what you can do about them.

A great deal of research has been done on this topic by Mark Stapleton, a mechanical engineer at Georgia Tech Research Institute. I'm grateful to him for sharing his findings.

Let me start by saying that most UDMA drives, perhaps the great majority, work fine under Windows. But there seems to be a discernable minority of UDMA drives that have been installed in systems that aren't quite capable of supporting the maximum speeds that UDMA can produce. Problems can be caused by electromagnetic interference on the system bus; poor flow control in hardware or firmware; or inferior circuitry on the drive itself. In such cases, a drive can "time out," slowing the system and/or corrupting data files.

The problem is affecting more and more people, because the installation of Windows 98 automatically installs UDMA drivers on systems with such drives. You can also install UDMA drivers under Windows 95 and Windows NT (Service Pack 3). And PC manufacturers may configure their systems so they ship with high-speed UDMA enabled, not realizing that this causes intermittent failures.

If you have a UDMA drive in a system that isn't quite up to speed (so to speak), you may experience one or more of the following difficulties when upgrading to Windows 98.

  • Win98 fails during the Plug and Play process and won't complete the installation.

  • Alternatively, after a successful installation, Win98 will start only in Safe Mode.

  • When transferring files, a drive appears to slow way down, then speed up again. This may also pause or hang software or your keyboard and mouse.

  • You start missing perfectly good files, or you lose the capability to access your hard drive at all.

  • Win98 shutdown takes much, much longer than normal.

Of course, the above symptoms can be caused by many other problems. One of the frustrating things about UDMA difficulties is that they may be intermittent and hard to diagnose.

To see if you have DMA or UDMA drives installed, click Start, Settings, Control Panel. Click the Device Manager tab, then click the plus sign to the left of "Hard Disk Controllers" to expand this branch. If you see an entry such as "Intel 82371AB/EB PCI Bus-Master IDE Controller," you have a UDMA-capable system. The entry "Standard Dual PCI IDE Controller" means you do not have bus-mastering drivers loaded.

To see if you have your system configured for DMA and UDMA, click the plus sign to the left of "Disk Drives," then double-click a drive icon, then click the Settings tab. If a "DMA" check box is present and it is checked, your system is configured to use DMA and UDMA transfers. If you have been having the problems listed above, you can try unchecking this box and restarting Windows to see if this helps.

For technical details, see a lengthy e-mail exchange between users of UDMA drives.

I'll have some good news about DMA and UDMA in next week's column.

Brian Livingston's latest book is Windows 98 Secrets (IDG Books). Send tips to He regrets that he cannot answer individual questions.

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