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All versions of Windows 98, 2000, and XP support DMA/UDMA modes. The exact steps required to enable DMA mode differ according to your chipset and the exact version of Windows you are using, as follows
- Windows 98/98 SE/Me
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The original Windows 98 release and Windows 98 SE are both identified as 4.10.1998, and both are supplied with a native DMA driver, as is Windows Me. Use that driver rather than the driver supplied by Intel or another chipset manufacturer. The Microsoft drivers require DMA support in BIOS, so you may need to flash your system BIOS to the latest version before installing the driver. Before installing the Microsoft driver, remove the Intel BM-IDE driver (if present) by running the BM-IDE installation program and choosing deinstall. To install the Microsoft driver,
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Right-click My Computer, choose Properties, and then click the Device Manager tab.
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Locate the CD-ROM drive and double-click it to display the Properties sheet.
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Click the Settings tab and mark the DMA checkbox in the Options section.
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Close the dialog and reboot the system.
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Redisplay the Properties sheet for the drive after rebooting to verify that the checkbox remains marked and that DMA is enabled.
Note the following considerations for Windows 98/98 SE/Me and DMA:
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On a clean install, we found that Windows 98/98 SE/Me automatically determines whether the chipset, drives, and BIOS support DMA. If so, DMA is automatically enabled by default.
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On an upgrade install to a system running Windows 95 OSR1 or earlier, we found that Windows 98/98 SE/Me Setup does not install DMA support, even if all required elements are present. If this occurs, you can enable DMA support by marking the DMA checkbox and restarting the system.
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On an upgrade install to a system running Windows 95 OSR2 or higher, we found that Windows 98/98 SE/Me Setup enables DMA only if Windows 95 had the Microsoft DMA drivers installed and enabled. If the drivers were not installed, or if they were installed but DMA was not enabled, Setup installs using PIO mode. Again, you can enable DMA support manually by marking the DMA checkbox and restarting the system.
- Installing Windows 98/98 SE/Me as an upgrade on a Windows 95 system running the Intel BM-IDE driver causes all sorts of IDE problems. The Intel BM-IDE driver version 3.01 has no uninstall option, but can be uninstalled using the version 3.02 or higher Setup program. Before upgrading to Windows 98/98 SE/Me, run BM-IDE version 3.02 or higher and choose the deinstall option.
- Windows 2000/XP
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Windows 2000 and Windows XP generally manage DMA properly and automatically. During a fresh install, Windows 2000/XP tests the ATA interface and the connected devices to determine DMA compatibility. If the interface and all connected devices are DMA-compatible, Windows 2000/XP enables DMA for that interface. A problem may arise during an upgrade installation, however. If the earlier OS version was not configured to use DMA, Windows 2000/XP may not enable DMA even though the interface and devices support it. To check DMA status on a Windows 2000/XP system, and to enable DMA if necessary, take the following steps:
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If you're not sure how your CD-ROM drive is configured, restart the system and watch the BIOS boot screen to determine whether the drive is connected to the Primary or Secondary ATA channel and whether it is configured as Master or Slave.
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Right-click the My Computer icon and choose Properties. Click the Hardware tab and then the Device Manager button to display the Device Manager.
- Locate the IDE ATA/ATAPI Controllers entry and click the + icon to expand the listing. There should be three lines visible, assuming that both IDE channels are enabled. The first, which will be something such as Intel® 82801BA Bus Master IDE Controller, is for the ATA controller itself. The two remaining lines should be Primary IDE Channel and Secondary IDE Channel.
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Right-click the channel to which your CD-ROM drive is connected, choose Properties, and then click the Advanced Settings tab to display the IDE Channel Properties dialog. This dialog has two sections, one for Device 0 (Master) and another for Device 1 (Slave). The listing for your CD-ROM drive should display the DMA mode currently in use in the Current Transfer Mode box. If it does, your drive is operating at peak efficiency, and you can exit the dialog.
- If the Current Transfer Mode box for the CD-ROM drive lists PIO Mode, check the setting for that device in the Transfer Mode box. If the drop-down list in that box is set to DMA if available, that means that Windows has determined that either the interface or the drive (or both) do not support DMA. Exit the dialog and resign yourself to running in PIO mode. If the Transfer Mode box is set to PIO Only, use the drop-down list to change that setting to DMA if available, save your changes, restart the system, and redisplay that dialog. If the Current Transfer Mode box for the drive now displays a DMA mode, the drive is now using DMA. If the box still displays PIO Mode, Windows has determined that it is unsafe to use DMA mode.
Regardless of operating system, it's a bad idea to configure a PIO-mode device to share an ATA channel with a DMA-capable device. That's because ATA doesn't allow mixing DMA mode and PIOmode on one channel. If one device runs PIO mode, both must do so, which cripples the DMA-capable device. In particular, it's a horrible idea to put a PIO-only CD-ROM drive on the same channel as an Ultra-DMA hard drive because that means the hard drive will run in PIO mode, which cuts throughput by half or more and dramatically increases CPU utilization. Put the PIO-only drive on its own channel, alone or with another PIO-only device, or replace the drive with a DMA-capable drive.
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