A "bottleneck" merely refers to the slowest factor in the system. The FSB is the bottleneck with the core system, and the hard drive is usually the bottleneck for the system as a whole.
Unless you can perfectly match up every component, there will always be bottlenecks. It's not that it's a bad thing, it's just the way it works. When you "eliminate the bottleneck", you generally create another, but just less of a bottleneck. If I swapped my IDE drives for 4 15k RPM SCSI drives in RAID 0, then that wouldn't be the bottleneck anymore. Maybe the network would, so I'd have to go to Gigabit. But then my Server wouldn't be able to keep up, so I'd upgrade that. Then the slowest component might be the RAM on my computer, so I upgrade that.
When you talk of a "bottleneck" in a system, it doesn't necessarily mean that that component needs to be upgraded, just that it's the slowest. There will always be a slowest component, that doesn't mean that you have to continuously upgrade.
(In theory you could match up all the components so they run perfectly together, but I don't see that ever happening in practice.)
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