Question

Mason asked about the advantages of a 64-bit processor.

Well, an obvious disadvantage is that you have to move more bits around. And given that memory accesses are a serious issue these days[1], moving around twice as much memory for a fair number of operations can’t be a good thing.

But how bad is the effect of this, really? And what makes up for it? Or should I be running all my small apps on 32-bit machines?

I should mention that I’m considering, in particular, the case where one has a choice of running 32- or 64-bit on the same machine, so in either mode the bandwidth to main memory is the same.

[1]: And even fifteen years ago, for that matter. I remember talk as far back as that about good cache behaviour, and also particularly that the Alpha CPUs that won all the benchmarks had a giant, for the time, 8 MB of L2 cache.

Answer 1

Most 64-bit programming environments use the “LP64” model, meaning that only pointers and long int variables (if you’re a C/C++ programmer) are 64 bits. Integers (ints) remain 32-bits unless you’re in the “ILP64” model, which is fairly uncommon.

I only bring it up because most int variables aren’t being used for size_t-like purposes–that is, they stay within ranges comfortably held by 32 bits. For variables of that nature, you’ll never be able to tell the difference.

If you’re doing numerical or data-heavy work with > 4GB of data, you’ll need 64 bits anyways. If you’re not, you won’t notice the difference, unless you’re in the habit of using longs where most would use ints.