Internet Explorer (IE) is able to upload files using the HTTP feature. By default IE uses a send buffer of 8 KBytes, which equals to about 80 KBytes per sec (KBps). It is possible to increase the size of the winsock send buffer, to speed up the uploading of larger files (ex. attaching files in web-mail).

Configure the size of the send buffer with this DWORD value:

[HKEY_CURRENT_USER \Software \Microsoft \Windows \CurrentVersion \Internet Settings]
SocketSendBufferLength = 16384 (Max - 65536)

More info MS KB329781

Note IE 7 does a better job when uploading, and does not require this registry setting.

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