Windows system will turn off the hard disk DMA mode

Text /Zhenyi

The DMA mode of the hard disk should be known to everyone, the hard disk PATA mode has DMA33, DMA66, DMA100 and DMA133, the latest SATA-150 They are all out! In general, most people still use the PATA mode hard disk. The DMA mode of the hard disk is 2~8 times faster than the previous PIO mode. The use of DMA mode has played a substantial role in the performance of the system. There have been many articles about how to open the DMA mode. I won't say much here.

But I found a new "problem" - Windows 2000, XP, 2003 system will sometimes turn off the DMA mode of the hard disk, automatically switch to PIO mode to run! This causes a sudden drop in the performance of the hard disk in the above system. The most obvious phenomenon is that the system startup speed is obviously slower. Generally speaking, the normal left-to-right slider of the Windows XP system starts up to 2~4. The secondary system can be started, but this problem may go 5-8 times or more! Moreover, when running the system, the hard disk operation obviously feels slow. When running some large software, the CPU usage often reaches 100% and pauses. When playing some large 3D games (such as Need for Speed ​​6), there is a significant pause ( Many people think that this is their own graphics card problem. Of course, if you are using the graphics card three years ago, it is a bit old to play these games, but if you use the GF graphics card that you bought this year, it is not a problem.) When the above problems occur, it is best to see if the DMA mode of your hard disk is turned off by the Windows system itself. Check if your system has DMA mode turned on:

1. Double-click "Administrative Tools", then double-click "Computer Management";
2. Click "System Tools", then click "Devices" Manager";
3. Expand the "IDE ATA/ATAPI Controller" node;
4. Double-click on your "Main IDE Controller";
5. Click on "Advanced Settings".

When you see "Device 0", the following transfer mode should be set to "DMA (if available)", then "current transfer mode", if "Ultra DMA Mode * (* is a number) , DMA33 is 2, DMA66 is 4, DMA100 is 5, DMA133 is 6)", then your system is normal, but if you set your own "Ultra DMA Mode 6" and did not change, it is now "Ultra DMA Mode" 4" or "Ultra DMA Mode 2" or "PIO mode" and can't be changed! It may be that the system has turned off the DMA mode by itself.

Analysis of the problem:

Well, let me first talk about how the problem is generated. There is such a setting in Windows 2000/XP/2003: Windows IDE/ATAPI port driver (Atapi.sys) cumulatively receives a total of 6 timeouts or cyclic redundancy check (CRC) errors, the driver will put the communication speed (Transfer mode) Substep down to the slower DMA mode from the fastest direct memory access (DMA) mode. If the driver continues to receive a timeout or CRC error, the driver will eventually reduce the transfer mode to the slowest mode (PIO mode). That's the problem! In general, a normal hard disk rarely has a timeout or cyclic redundancy check (CRC) error, but when we use the suspend (also called hibernation) in these systems and recover the computer, it is easy to cause timeout or cyclic redundancy. Inspection (CRC) error. Because the system sets the timeout value to 4 seconds, when the system makes a read request to the ATA disk, if the hard disk response time exceeds the timeout value of 4 seconds, a timeout or cyclic redundancy check (CRC) error will occur, but because the system is When the hang (also called hibernation), the hard disk is in the stall state. When the computer is restored, the hard disk has a process from stop to movement, which easily causes the timeout value of most hard disk response times exceeding 4 seconds. This means that when we use the computer to suspend 6 times, the system will reduce the communication speed (transfer mode) from the fastest direct memory access (DMA) mode to the slower DMA mode. If it is suspended more than 6 times, the driver will eventually reduce the transfer mode to the slowest mode (PIO mode). This is why the Windows system suddenly slows down.

Solving Problems:

To re-enable the transfer mode for a typical DMA or faster DMA for an affected device, do the following:
1. Double-click Administrative Tools, and then double-click Computer Management;
2. Click System Tools, then click Device Manager;
3. Expand the IDE ATA/ATAPI Controller node;
4. Double-click the controller for which you want to restore the typical DMA transfer mode;
5. Click the Driver tab;
6. Click Uninstall.

When this process is complete, restart your computer. When Windows restarts, the hard disk controller is re-enumerated and the transfer mode of each device connected to the controller is reset to the default value.

But this is just to reset the transfer mode of the hard disk device to the default value. When we use the suspend system again, the system will turn off the DMA mode by itself! So we have to do the following:

1. Click Start, click Run, type Regedit, and then click OK.
2. Locate and click in the registry:
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlClass{4D36E96A-E325-11CE-BFC1-08002BE10318}