浏览器对同一个域名可以并发请求，下面是每个浏览器默认的并发数限制
| Browser | HTTP/1.1 | HTTP/1.0 |
| IE6,7 | 2 | 4 |
| IE8 | 6 | 6 |
| Firefox2 | 2 | 8 |
| Firefox3 | 6 | 6 |
| Safari3,4 | 4 | 4 |
| Chrome1,2 | 6 | --- |
| Opera9.63,10.00 | 4 | 4 |