什么设置可能导致AMP服务器每个浏览器一次只允许1个请求？

I'm using an AMP server (Apache 1.3, MySQL 5.0, PHP 5.1.5) which I have found to only allow 1 connection/request per browser at one time. The easiest way to reporduce this is to request a large download which is passed through PHP and try to access another page at the same time. You will end up waiting for the first request (the file download) to complete before the other page loads.I'm using an AMP server (Apache 1.3, MySQL 5.0,