It's because you're using 10.5, last of the great OS-X's. Performance requirements went up in 10.6 and WAY up in 10.7. I have an old MBPro running 10.5 and it consistently feels faster (and is provably far more stable) than my new model work machine running 10.7
Really? Glad in many ways I am still using 10.5 then. I've no problem with stability. As you mention it seems quite rock solid.
I had no idea that the memory requirement for 10.6 or 10.7 was so high (I've heard anecdotal comments from non-tech friends). But then I'd also heard the official Apple line that 10.6 was meant to be better at memory management and slightly faster than 10.5 because the binaries were no longer dual PPC and Intel -- just Intel.
So, in God's name, why are the later versions so resource hungry?
10.6 switched the architecture from i386 to x86-64. Since many third party applications were still i386 binaries at the time of its release, both versions of every system library had to be loaded. That did increase memory use in some ways, but it's not really a problem anymore unless you use Word 2008.
But that's about it; 10.6 is much faster and more stable in every other way, that being the entire point of the release.
Of course, I should say 'was', since it's not even the current version. Unless you're posting from a time warp.
