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February 2, 1998

Microsoft plans a fix for Internet download speeds

Developers at Microsoft are changing the forthcoming Windows 98 to improve users' Internet download speeds across modems. I wrote in my columns of July 21 through Aug. 11, 1997 about the problems caused by Windows 95's defaults. (See our Printlinks page.) Windows 95 uses a Registry setting that can be inefficient for Internet downloads. Specifically, the Registry sets a value called MaxMTU (which stands for Maximum Transmission Unit) to 1500. This is a good value for people who access the Net through a LAN but a poor one for people who use a modem.

To its credit, Microsoft seems to be changing the defaults in Windows 98. Last week, Microsoft Windows developer Mike Zintel confirmed that Win98 will default to a more efficient MaxMTU value of 576 if it detects an Internet connection slower than 10Mbps. In other words, Win98 will use a different default if the user is on a LAN (1500) than the default used for a dial-up modem (576). The value 576 is a widely used Internet standard.

Why is this important? Users who changed their settings based on my earlier columns have reported improvements of as much as double their former speed. The difference is only noticeable, however, on a relatively lightly loaded server, and then only in some cases.

Tracking down why the MTU setting speeds up some downloads is tricky. The behavior depends on Internet conditions and is thus difficult to reproduce. Microsoft representative Zintel, however, suggests three reasons why MTU might affect throughput.

  1. As line errors increase on an Internet connection, a smaller MTU such as 576 makes re-transmissions faster than a larger MTU such as 1500.

  2. When you are running an asynchronous application, such as video, across the Internet, a larger MTU can make your system feel less responsive.

  3. Certain servers do not implement the IP's re-transmission algorithms well, and benefit from a smaller MTU.

If you don't want to wait for the release of Win98 to fix this problem, you can change your Windows 95 defaults now. Because the process of editing the Registry in this case is complex, I recommend you use a utility to handle the changes.

TweakDUN 1.2 by Patterson Design Systems and NetPro Northwest changes your Dial-Up Networking settings in the Registry to a variety of possible defaults. The registered version costs $12.50. You can download a copy from and then pay by credit card or Cybercash. You must have Visual Basic 5.0 DLL files, which are available from the same Web site.

A freeware utility, MTU-Speed Pro 4.03, by Mike Sutherland, is available at (Sutherland currently requests a voluntary $10 donation.) MTU-Speed can use your ping utility to detect the optimum MaxMTU setting for your particular Internet connection. This is valuable because some ISPs use an MTU value other than 576, and you should conform to their value.

To get the most out of TweakDUN or MTU-Speed, be sure to first read the explanatory files located at NetPro Northwest's site,

Brian Livingston is the co-author of several best-selling Windows books, including the most recent Windows 95 Secrets (IDG Books). Send comments to Unfortunately, he cannot answer individual questions.

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