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modem speed up on com 2 ?

Posted on 1998-02-01
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Last Modified: 2013-12-27
I've been told that Com2 runs faster than the other com ports and it would be a good idea to have my modem run on com2 instead if com4 as it is at the moment. But i only want to do this if it's worth it as my mouse is currently using com2 and my modem is NOT plug'n'play!!!
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Question by:arint
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by:nebworth
ID: 1145247
  I've never heard that,and I don't see why there would be a problem these day.  Once upon a time, maybe, when com4 wasn't natively supported by DOS...  If you are using com2 for your mouse, then don't use com4 unless you are planning to use a different interrupt...  Let me explain.  The addresses that software typically looks at for com data are 3f8, 2f8, 3e8, and 2e8, but the interrupt that software typically looks at are 4, 3, 4, and 3 again.  This means that a typical com2 device and a typical com4 device will share the same irq.  That means when you use a mouse on com2, and you have a modem on com4, then when you try to communicate with your modem, you lose track of your mouse.
   Of course, Windows will allow you to use any interrupt with your modem, and most modems will allow you to change your interrupt, but for backward compatibility with DOS programs, I would recommend sticking to one of the normal com port settings. com1 (3f8, 4) is a very popular spot for modems on many brand name computers, but you must make short that you don't already have a modem or com port occupying this spot.  If you do, you can always disable it if you know how.  com3 (3e8, 4) is the alternative and works fine for everything out there today.  
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by:magigraf
ID: 1145248
Nebworth...

Why didn't you post that as an answer??
Looking to lose points??
Regards
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nebworth earned 50 total points
ID: 1145249
I've never heard that,and I don't see why there would be a problem these day. Once upon a time, maybe, when com4 wasn't natively supported by DOS... If you are using com2 for your mouse, then don't use com4 unless you are planning to use a different interrupt... Let me explain. The addresses that software typically looks at for com data are 3f8, 2f8, 3e8, and 2e8, but the interrupt that software typically looks at are 4, 3, 4, and 3 again. This means that a typical com2
 device and a typical com4 device will share the same irq. That means when you use a mouse on com2, and you have a modem on com4, then when you try to communicate with your modem, you lose track of your mouse.  Of course, Windows will allow you to use any interrupt with your modem, and most modems
will allow you to change your interrupt, but for backward compatibility with DOS programs, I would recommend sticking to one of the normal com port settings. com1 (3f8, 4) is a very popular spot for modems on many brand name computers, but you must make short that you don't already have a modem or com port occupying this spot. If you do, you can always disable it if you know how. com3 (3e8, 4) is the alternative and works fine for everything out there today.

    Thanks, Magigraf, for your encouragement...  I just wanted to be more sure I deserved them...
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by:arint
ID: 1145250
Like i thought. Don't think i'll bother changing anything as it all works ok at the moment.
Cheers
       Andy
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