How come 2 concurrent calls to apache2 not processed in parallel?

echo "Start: ".time();
echo "<br/>End: ".time();

Open 2 tabs into chrome, and visit script. (same time)

Derive from TAB 1

Start: 1321331382
End: 1321331387

Derive from TAB 2

Start: 1321331387
End: 1321331392

How do you stop this from happening?

The questions you have suggested right answer.

session.auto_start = 1 was triggered in php.ini The answer would be to either start script with : session_write_close()

or session.auto_start = into php.ini.

Appreciate the assistance.

If you use Chrome and ask for exactly the same resource in multiple tabs, it'll wait for a resource to complete installing in a single. This is because when the headers allow, the 2nd tab will load from cache, instead of reloading it in the server.

It has nothing related to your server configuration, but more related to your problematic test method. Fire off a few wget calls in the command line, and will also likely act as expected.

You may also verify this is going on using a debugging proxy, for example Fiddler, or packet sniffing at software, for example Wireshark.

What exactly are your apache configurations? It is possible you will find the config set to simply run 1 server rather than multiple servers. Therefore if it were set this way then it might be impossible to operate at the same time.