DADDY BOB'S COMPUTER Q & A

January 13, 2008

Q. For some reason, my DVD burner has slowed down to a  burning speed that is a fraction of what it used to be. Does my DVD burner need replacing? If not, what could have caused this slow down, and how can I get my burning speed back?

A. The slowdown is probably not caused by a defective DVD burner and if it is working OK other than the speed, it is probably not defective. I suspect that the "Transfer mode" of the DVD burner has changed from Ultra DMA (Direct Memory Access) to PIO (Programmed Input/Output).  This is going to take some explanation and I'll try to keep it as short and un-technical as I can.

In the PIO mode, the CPU acts like a middleman in the data transfer. The process goes something like this. The CPU asks the DVD drive for a byte of information. The DVD drives gives it to the CPU and then the CPU sends it to the memory and checks to be sure it has transferred successfully. This process is repeated until all the data has been transferred. This ties up the CPU, and is time consuming.

In DMA mode it goes something like this. The CPU tells the DVD drive to send all the information directly to memory, and notify it when it is finished. The DVD drive than communicates directly with the memory, eliminating the CPU middleman, making the transfer much faster. This also allows the CPU to be doing something else while the data is being transferred.

One quick technical note here. Ultra means that it is using double transition clocking. Before Ultra DMA (UDMA), one transfer of data occurred on the rising edge of each clock cycle. With Ultra DMA, data is transferred on both the rising and falling edges of the clock. If you don't follow this, just remember that Ultra DMA is about twice as fast as regular DMA transfers.

Here is a table of the current UDMA modes and their corresponding speeds. Only modes 2, 4 and 5 have ever been used in drives.

Note: In common terms, drives that use Ultra DMA are often called "Ultra ATA/xx" where "xx" is the speed of the interface. So, few people really talk about current drives being "Ultra DMA mode 5", they say they are "Ultra ATA/100".

To use Ultra DMA modes over 2, a special, 80-conductor IDE cable is required. This cable uses the same 40 pins as the old cables, but adds 40 ground lines between the original 40 signals separating them from each other and preventing interference and data corruption. Whew!!! I hope you got all of that.

Now, to answer your original question.

Windows XP reverts to PIO (Programmed Input/Output) mode after several attempts to use DMA mode have failed. If this happens, Windows XP will not return to DMA mode even if you tell it to do so. Microsoft considers this a safeguard, although I wonder just what it is protecting.

Here's how to check or change the transfer mode: (This example is for XP. Vista is similar but the dialogs are slightly different.)

1. Right Click My Computer or press the Windows + Pause keys
2. Click the Hardware tab
3. Click the Device Manager button
4. Click the + in front of IDE ATA/ATAPI Controllers
5. Right Click on the Secondary Channel. (Normally it is the secondary channel that is used for the CDs on a computer that uses all IDE devices. If the computer has a SATA hard drive and IDE CDs, then it may be the Primary Channel. If the computer uses SATA for the hard drives and CDs, there will be no entry in the Device Manager for the IDE ATA/ATAPI Controllers)
6. Click on Properties
7. Click the Advanced Settings tab and this dialog will display.

The CD drives will be designated as Device 0 or Device 1. To determine which of your drives are device 0 or 1.

1. Open the Device Manager per the above steps

2. Click the + in front of “DVD/CD-ROM drives”

3. Right Click the device to check

4. Choose Properties. The device number is shown as the Location.

Unsuccessful attempts to use UDMA may have caused the "Current Transfer Mode" mode be locked in the PIO mode as described above. In that case, there are a couple of ways to restore the DMA mode.

One is to try to do a System Restore. For instructions on how to do a System Restore, click HERE. NOTE!! If there have been any operating system changes, new software installations, virus or spyware scans or program updates since the last System Restore was created, this may also undo then. Therefore, a System Restore to a previous point may not be desired.

The other way is to uninstall and then re-install the CD drive in question. Windows will then allow you to set the transfer mode to DMA, and Windows will use that setting. Of course, if there is a real problem using DMA mode, Windows will revert to PIO mode again.

Here's how to uninstall and reinstall the CD drive:

1. Open the Device Manager

2. Click the + in front of DVD/CD-ROM Drives

3. Right click the drive in question

4. Click Uninstall. The drive will be uninstalled

5. Highlight the top item in the list

6. Click Action from the menu

7. Click Scan for Hardware Changes The drive will be re-installed.

Assure that the transfer mode is set to "DMA if available" and this should return the DVD burner to its original speed.

Most new computers are replacing the IDE interface with the SATA interface, and SATA as currently implemented, doesn't use DMA.

Click HERE to view or download as a Microsoft Word document