The maximum number of concurrent HTTP connections allowed to a web
server is controlled by the browser. The HTTP 1.1 specification suggests
a limit of 2 connections per host, but this requires further
consideration if persistent connections are to be used. Some browsers
can be configured to accept more, but your users will more than likely
have the default settings. IE honors the 2 connections per host
suggestion (but to change this you have to edit the registry, see
MaxConnectionsPerServer). Firefox sets this value to 8 but does still
limit persistent connections to 2 (you can change these settings via
about:config).
If you were dealing with a closed network or intranet application, you
may be able to change your company's IT policy and roll out different
default settings, but for public applications I doubt this will be
possible. There are lots of other tricks that you can use to optimize
HTTP requests (e.g. idempotent GET requests you benefit from pipelining
etc)... but my point is that there's a bit more to consider than a bunch
of simultaneous requests.
