DCOM用的,参考www.microsoft.comtechnet/iis关于iis5配置的文章.

Tip 9: Out-of-Process Execution Trades off Performance for Reliability
Both ASP and MTS/COM+ have configuration options that allow you to trade off reliability for performance. You should understand these trade-offs when building and deploying your application.
ASP Options
ASP Applications can be configured to run in one of three ways. With IIS 5.0, the terminology “isolation level?has been introduced to describe these options. The three isolation level values are Low, Medium, and High:
Low Isolation. This is supported in all versions of IIS and is the fastest. It runs ASP in Inetinfo.exe, which is the primary IIS process. If the ASP application crashes, so does IIS. (To restart IIS under IIS 4.0, Webmasters would monitor the site using tools such as InetMon, and fire off batch files to restart the server if it failed. IIS 5.0 introduces reliable restart, which automatically restarts a failed server.)
Medium Isolation. IIS 5.0 introduces this new level, which is referred to as out-of-process, since ASP runs outside of the IIS process. In Medium isolation, all ASP applications configured to run as Medium share a single process space. This reduces the number of processes required to run multiple out-of-process ASP applications on one box. Medium is the default isolation level in IIS 5.0.
High Isolation. Supported in IIS 4.0 and IIS 5.0, High isolation is also out-of-process. If ASP crashes, the Web server doesn’t. The ASP application is automatically restarted on the next ASP request. With High isolation, each ASP application that is configured to run as High runs in its own process space. This protects ASP applications from each other. Its drawback is that it requires a separate process for each ASP application. This can add up to a lot of overhead when dozens of applications need to be hosted on one box.
Which option is the best? In IIS 4.0, there was a fairly steep performance penalty for running out-of-process. In IIS 5.0, a lot of work was done to minimize the cost of running ASP applications out-of-process. In fact, in most tests, ASP out-of-process applications in IIS 5.0 run faster than in-process applications in IIS 4.0. Regardless, in-process (Low isolation level) still produces the best performance on both platforms. However, you won’t see much benefit to the Low isolation level if you have a relatively low hit rate or low maximum throughput. Therefore, you should not feel the need to reach for the Low isolation level until you need hundreds or thousands of pages per second per Web server. As always, test with multiple configurations and determine which trade-offs you are willing to make.