Comment by ffk | Hacker News Reader

Comment by ffk | Hacker News Reader

"But now Apple can also claim an advantage in raw horsepower. The new 64-bit A7 chip is the smartphone equivalent of a big V12 engine."

Except these performance gains most likely would of been seen on a 32 bit version of the chip.

It's interesting to see how much marketing is put around 32 vs 64 bit chips and the effect it has on how people market. The biggest benefit is the ability to access more than 4GB of memory. For reference, the iPhone 5S has 1GB of memory. Eliminating the need for PAE and other expensive workarounds is definitely a bug plus. i64 and cheap doubles are certainly a bonus too.

I suspect the primary reason for moving to 64 bit is not for performance gains now, but for future compatibility. Eventually, the iPhone 5S will be the oldest supported iPhone and running a 64 bit processor will reduce maintenance costs of needing to maintain a 32 and 64 bit line of software.

I think this would be a much more informative article if the author had interviewed a few experts to discuss the benefits of 64 bits over 32 bits rather than just say they go faster which at this point is debatable.

> It's interesting to see how much marketing is put around 32 vs 64 bit chips and the effect it has on how people market.

It's because it's a much more approachable pitch than "we doubled the size of the reorder buffers and added another instruction dispatch port." In Apple's case, they're simply using "64-bit" as a proxy label for all the other architectural improvements in Cyclone.

> The biggest benefit is the ability to access more than 4GB of memory. For reference, the iPhone 5S has 1GB of memory.

No. The biggest benefit as having an addressable virtual address space which is in the tera/peta/exa byte range. Which makes a lot of things simple and efficient, even if you don't have a lot of physical memory. Read about e.g. LMDB's design or Varnish's design for good examples.

The other significant benefit is more registers.

I'm familiar with this, which is the reason I mentioned "PAE and other expensive workarounds" which allows you to break the 4GB limit.

It was badly worded on my part, I was in a hurry. :)

Or is the biggest benefit in this scenario the expanded availability, in 32bit mode, of registers, so that programs compiled for such a processor execute on-core significantly more than those not compiled for such a machine?

Registers are referenced explicitly, already compiled software could not possibly use more registers than it already does.

http://en.wikipedia.org/wiki/Register_renaming

Reply on news.ycombinator.com