In Internet Explorer 7 and earlier, the maximum number of concurrent connections per host process to a single server via HTTP 1.1 is 2. For HTTP 1.0, the limit is 4. IE8 increases the HTTP 1.1 limit to 6.

The number of http connections affects how many simultaneous downloads one can perform, and the number of simultaneous AJAX requests.

Create the following DWORD value to configure the connection limit:

[HKEY_CURRENT_USER \SOFTWARE \Microsoft \Internet Explorer \MAIN \FeatureControl \FEATURE_MAXCONNECTIONSPERSERVER]
iexplore.exe = 10

More Info AJAX - Connectivity Enhancements in Internet Explorer 8
More Info MS KB282402