Tech Talk (03/01)
Speeding up your hard disk
by Brian K. Lewis, Ph.D.*
Member of the Sarasota Personal Computer Users Group, Inc.
This really wasn't the topic I had originally planned for this month's Tech Talk. However, Fred Langa (Byte Magazine, Windows Magazine) published a topic in his newsletter that seemed to be very appropriate. His newsletter said that anyone with an IDE hard drive of recent vintage could greatly increase its data transfer speed by turning on the DMA setting in Windows device manager. There was a caveat. If the drive or the BIOS couldn't handle the DMA setting, you might not be able to get back into Windows! Naturally, that might create some problems. Primarily, just how would you get your computer operational again? Just another reason to have a good backup before making major changes to your system.
Why is increased hard disk data transfer of any interest at all? The answer is that this is the main bottleneck in your computer's function. Transfer of information to and from the hard disk is just about the slowest operation in your system. Several IDE data transfer standards are currently in existence. There are PIO transfer modes, DMA transfer modes and UDMA transfer modes. The PIO modes range from 3.33 megabytes per second (MB/s) to 16.67MB/s. The DMA transfer modes range from 4.16MB/s to 16.67MB/s. On any Pentium computer, the system bus and the memory are capable of moving data considerably faster than this.
So, what's the difference between these two modes in actual practice? To start with, DMA means direct memory access. Essentially, that means the data transfer occurs directly between the hard drive and the RAM memory, bypassing the central processor (CPU). Reducing the load on the CPU allows processing cycles for other functions. So even with similar data transfer speeds, the DMA mode allows the processor to handle other work and the overall system operates faster. That means things such as loading a program from the hard disk into RAM will take less time.
The newest mode is UDMA or Ultra-DMA. The UDMA mode has transfer times of 16.67 to 66.67MB/s. Now we are looking at something that is considerably faster than the other two modes. You will see hard drives advertised as being UDMA-33, UDMA-2, ATA-4, or ultra ATA/33 compatible. These terms are all equivalent. There are also drives marked as UDMA-66, UDMA-4, ATA-5, or ultra ATA/66. These hard drives will work at the higher speeds only with computers that have a compatible BIOS, EIDE motherboard connectors that accept UDMA-33 or UDMA-66 and Windows 98/2000/ME. Windows 95 won't work without a specific DMA driver from the computer manufacturer and then only with UDMA-33. These drives will work in PIO mode with any computer system. That means a much slower data transfer rate.
Microsoft provides, in their KnowledgeBase, a small program that can be used to test whether or not your hard drives will work in DMA mode. However, in my opinion, this test is not for the casual user. It involves booting your computer into DOS mode, not a DOS window. Then running the program "Debug" and entering a series of hexadecimal codes. Then if the correct error code is returned, this is evidence that your drive will work in DMA mode.
There is another way to check if your computer is UDMA compatible. When your computer boots and, just after it completes the memory check, it identifies your hard drive(s). With the more recent AMI BIOS, it will show on the screen if the drive is UDMA-2 or UDMA-4 compatible. Any UDMA/66 drive will work quite high well on a UDMA/33 connection, it just can't reach the maximum burst speed of 66 MB/s. In order to achieve this maximum transfer rate, the drive must have a special UDMA/66 cable connecting it to the motherboard, in addition to the other requirements of BIOS and operating system support.
Windows Magazine maintains a computer-testing program on their Website called "WinTune". This tests many components of your computer while you are online and compares the results to similar systems. Since both of my IDE hard drives tested as DMA compatible and the BIOS said they were UDMA-2 drives, I decided to do some on-line testing. First, I ran WinTune on the drives in the non-DMA mode. Then I changed the DMA setting, rebooted the computer and re-ran the test. To further compare the results I went to PCPitStop and used their computer analysis program to test my drives. I found the results rather confusing. The results are given in Tables I & II. The data transfer rates are in megabytes per second.
When I looked at these results, it was obvious that the only change was in the uncached speed. It was also obvious that this speed was nowhere close to the 33MB/s that would be expected. The cached speed was so much greater than 33MB/s, that I didn't believe it. So, I ran WinTune's advanced hard drive analysis. This tests transfers of various file sizes from 128 KB to 65,536KB. Here the transfer rates ranged from 113MB/s to 5MB/s. Although they decreased with increasing file size, they still didn't look like real world transfer rates. Nothing I found indicated that it was possible for a UDMA-2 drive to transfer data in excess of the burst rate of 33MB/s. If the DMA setting only affected the uncached transfer speed, then it really wasn't worth the effort to make the change.
So, I tried another approach. I downloaded a small hard drive test file called HD Tach. This is a shareware program. It will test only the read capability of your drives unless you pay the fee and register the software. I tested both of my IDE drives with the program in DMA mode and in non-DMA mode. The results are shown in Table III.
You will note that the burst speed of these drives increased dramatically after the DMA mode was turned on. In addition, the CPU usage dropped as well. These results, I believe are more representative of the effect of changes in DMA than the tests shown in the other two tables. Although these results do not reflect the maximum speed capacity of the UDMA standard, they are probably closer to the real world results you will see on your computer. The change in CPU usage is probably the most important change produced by using a DMA mode. (For those that are statistically minded, yes, these are averages of several runs.)
So, should you be trying to set up the DMA mode on your computer? First, you need to be certain that your drives, your BIOS and your operating system will support this mode. If you are running Windows 95, I wouldn't even consider it. Second, if you can't see the boot information, then I suggest you try going into the BIOS setup mode and see what you can learn about your drives and their capability. It's also possible to check the drive manufacturer's web site to see if the specifications for your hard drive include UDMA. If all this checks out, then you can consider making the change. Start by right-clicking "My Computer" and select "Properties." Click on the "Device Manager" tab and then the plus sign by the drive list. Next, open the "Properties" window by double clicking your drive. Finally, click the Settings Tab. If there is no check mark in the DMA box, check it, then click OK until you are out. Windows will inform you that you need to restart your system. When the system has rebooted, check the DMA box to insure that the check mark is still there. If it is not, don't try again. Your system is probably not fully DMA compatible.
This change will improve the data transfer handling on compatible computer systems. However, don't try it on your computer unless you are absolutely certain your system is fully DMA capable and only after you have done a full backup. Who knows, you may have to restore the original DMA settings by restoring your hard drive.
*Dr. Lewis, a former university & medical school professor, is a computer consultant doing instruction, hardware/software services and system upgrades.
He is available to help you with your home or business computer problems. He does make house calls and can be reached via e-mail at brian_klewis@hotmail.com or voice mail at (941) 925-3047. Note: there is an underline between the n and the k (n_k) in the email address. :
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