What makes a 64bit processor faster than a 32bit processor?

[Nsof]

Assuming OS and applications are compiled for the correct architecture why would a 64bit processor/os/app be faster than a 32bit processor/os/app?

Larger address space is one potential reason.

Is large integer math a factor?(I don’t think so.)
Is floating point arithmetic a factor? (Also don’ think so)
Is larger data bus also a factor? (due to less reads? Perhaps I should first ask if the data bus is indeed bigger)
A larger instruction set?
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[jesternl]

Every CPU cycle a 64-bit CPU can handle twice the amount of data. It can also keep more data easily available, so there is less swapping if bits in and out of memory, which again leads to faster instruction handling, since no cycles need to be wasted on keeping track of where the correct data is.

Probably more, but that is what I can remember off-hand.

The instruction set is 'baked in' to the CPU, and makes no difference I believe.

[MNOWAX]

I'm out of my element here, all i know is that 64 bit prcessors allow for more RAM allocation and use.

I'll let guys like Zag take this one...
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[Nsof]

[Antrax]

Basically, more registers and wider ones. 32 bit "eax" becomes 64 bit "rax" and similarly for other "named" registers, and you get R8-R15 in addition.
There are some other minor changes (calling conventions) but that's the "free" speedup you get.

[edit]
One thing you need to know is that 32->64 is not 2x speedup, even potentially. This isn't like moving from SSE to AVX or from a dual-core machine to a quad-core. I don't remember the exact figure, but it's a few dozen % at peak.
Also, I do multithreaded optimization these days
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[Zag]

[extropalopakettle]

As jesternl and Antrax mention, more registers allow more variables to be kept in CPU without loading values from and storing to memory. 64 bit machines generally have more registers, but I think this is an improvement that's independent of their being 64 bit wide.

The larger address space certainly allows greater performance for some applications, where a large working data set can be kept in RAM rather than swapped in and out from disk. A large database, especially if mostly or purely read-only (or where writes need not be synced immediately) is a common example.

There are also many cryptographic algorithms (and perhaps others) that do a lot of weird seemingly random bit level stuff - XORs, bit rotations (shifts left and right), etc, and these can be adapted to run much faster (much less instructions executed) with 64 bits at a time than with 32.

[extropalopakettle]

[Antrax]

Sorry to disappoint, then.
In any case, I thought the question was practicality-oriented, not theoretically-oriented. The only theoretical gain from 64 bit addressing vs. 32 is being able to have more ram (though I guess you could probably gain something on the cache/TLB fronts as well). In reality, though, 64 bits processors came with additional registers and extended the existing ones. I think the latter is a result of the current processor design (though I'm far from an expert on that), but I'm pretty sure the former is just coincidental, as others have said.

Zag, to answer your question, there's plenty of registers for everyone - though some you can't really use (the CRs, most MSRs) and some depend on the underlying SIMD architecture (MM/XMM/YMM). I was referring to the GPRs in particular, sorry for not making it clear.
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[jesternl]

[Antrax]

Not really, what Zag's describing is a cache miss more than anything. Register pressure is akin to trying to cook in a very small kitchen - you'll always have to move things around since your counter can't fit them all.
A branch misprediction is like completing someone's sentence and having them get pissed off because that's not what they meant. You waste time being chewed out for trying to guess instead of just listening, and then they repeat the whole thing anyway.
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[Zag]

Nice analogy! And my wife does that to me all the time!

[Antrax]

Thanks. It's actually kind of fun. See if you can recognize these microarchitectural (well, technically only 2 are) issues:

a) There's someone with the same name as you living close by. As a result, your mail takes forever to reach you, as you first have to wait for the mailman to send it to the other guy, then go over there to sort things out.
b) Your phone only has ten entries under speed dial, but you have twenty friends and they all complain if they're not on it, so whenever you go to visit one of them, you have to spend time looking up their number and putting it under speed dial.
c) You're a frequent flier but so's the elderly gentlemen in front of you in the express boarding lane, and he's taking forever to find his boarding pass and asking a million questions, leaving you to look enviously at the lucky passengers who bought economy.
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After years of disappointment with get rich quick schemes, I know I'm gonna get rich with this scheme. And quick!

[MNOWAX]

you see I'm come from twenty years of trial and error, not formal education, so my knowledge is very spotty when it comes to stuff that wouldn't be used in experiences of fixing computers

Nice to know who i can send questions like that to.
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