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August 4, 1997

Free utility, readers' test results can help improve Net download speed

Two weeks ago, I wrote about the fact that Windows 95 uses default values that can seriously hurt your throughput when accessing the Internet via a modem. A change of two Registry keys, however, can immediately improve your throughput, cutting download time in half for some Windows users. (See "Double your Net download speed with MaxMTU," July 21.)

I've received messages since then from scores of readers who have tried changing these two settings. About half report throughput improvements ranging from 15 percent to 100 percent or more. The other half report no difference or, in some cases, even reduced throughput.

The InfoWorld Test Center is in the process of running a series of routines to determine the optimum relationship between these settings and dial-up Internet throughput. I'll report on those findings when they're available. But in the meantime, there's no reason not to use the improved settings on your PC if they reduce your download time.

Unfortunately, the Web site that originally posted two simple .REG files that helped users make these changes has removed them since my column appeared. In place of the .ZIP file I cited, a new .ZIP file appeared with instructions on downloading a $10 application to make the changes.

Charging money for a utility is OK with me, but in this case you can easily download a new, free utility that does the same thing. MTU-Speed was developed by Mike Sutherland and is available from

MTU-Speed changes the two Registry settings I described on July 21, which are called MaxMTU and RWin. MTU stands for Maximum Transmission Unit. The Internet standard packet size is 576 bytes. MTU-Speed sets MaxMTU to this value.

Windows 95 defaults to a MaxMTU value of 1500, which is the value used on Ethernet LANs. If you access the Internet through a LAN (as opposed to a modem or dial-up connection), you should leave MaxMTU at its default setting. If your Internet service provider uses a different MTU than the Internet standard, you should set MaxMTU to the value your ISP uses.

RWin stands for the Default Receive Window. This value should usually be four times larger than MTU minus 40. For a MaxMTU value of 576, your RWin should be 2144.

MTU-Speed sets MaxMTU to 576 and it also provides a slider bar to set RWin to different multiples of MTU minus 40. Set RWin to a multiplier of four, click MTU-Speed's Update Registry button, then restart Windows. After this, an RWin multiplier of six, eight, or 10 may or may not improve your performance even further.

Neither of these changes will improve your throughput from a Web server that is bogged down by too many requests. You'll see improvements only from servers that aren't overloaded. If you see no benefit at all you can click the Remove All Settings button in MTU-Speed and you'll be back to normal.

Note: If you don't have the Cfgback.exe utility I mentioned in my July 21 column, you can copy it to your Windows folder from the \Other\Misc\Cfgback folder on the Windows 95 CD-ROM.

An even better utility is Eru.exe, which you can copy from the \Other\Misc\E0ru folder on the CD. It is also available from Microsoft at Store the downloaded Eruzip.exe file in a temporary folder, then run it once to extract Eru.exe. Run this Emergency Recovery Utility to back up your Registry.

Brian Livingston is the co-author of Windows 95 Secrets and four other Windows books (IDG Books). Send tips to or fax: (206) 282-1248.

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Copyright © 1997 by InfoWorld Publishing Company


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