Bruce Stephens wrote:
Tom Anderson writes:

[...]

On the flip side, the 64-bitness of the registers only gives a speed
boost to code that specifically needs to manipulate wide operands -
cryptography, scientific computing, perhaps some SIMD-based graphics
operations. For most use today, 32-bit+PAE should be faster than
64-bit. And yet, the market has moved almost entirely over to
64-bit. Grr.

IIUC the 64 bit instruction set has lots more registers (not just bigger
ones), and that's a significant benefit for lots of applications.

[...]

64 bit code is a bit larger, because it carries 64 bit entities...but
that's usually more than made up for by the faster speed of computation.

Linux wise the only real downside is dealing with legacy 32 bit code
which doesn't always work, especially if its a 3rd party kernel module :-(