We hope that our description of the replay system managed to fill the informational vacuum around one of the most interesting and mysterious subsystems of the Pentium 4 CPU.
We believe that this information must be revealed at least in the micro-architecture descriptions and optimization guides: those who tend to optimize their software for maximum performance should know about the “hidden dangers” of this process.
On the other hand, we do understand why Intel didn’t do it: they would hardly manage to describe replay without making a negative impression on the potential customers. And the negative impression is definitely what any commercial corporation is hunting for. Unfortunately, their strategy in this respect, namely concealment of the replay existence, is also not the most reasonable thing to do. There is a very thin border between marketing and deceit, and it looks like in this case marketing seems to have crossed it.
Unfortunately, replay affects the Pentium 4 processor performance in a negative way. The only thing that justifies its existence is the fact that Pentium 4 processor will not work correctly at all without the replay.
Anyway, we are not going to stop here and we intend to continue investigating the Pentium 4 mysteries. It is simply time to take a break and to look back: what have we achieved during the past year of hard work? Which way shall we take in our further investigations? What tasks shall we set for our study of Pentium 4 architecture?
Some tasks have already been set, actually. For example the launch of Pentium 4 6xx series made it very important to find out how effectively the 64-bit instructions support has been implemented there? And we are already working on it. Hopefully we will be able to share some results with you soon enough.
There are still questions left about the replay, so we will continue investigating a few pretty interesting sides of this mechanism.
Anyway, there are still a lot of things we could dig in. It is even sad in a way that the second article pf the trilogy has come to an end :)
Stay tuned for the next part of our detailed investigation, which will be called Replay: Unknown Peculiarities of the NetBurst Core!