The iPhone 5S uses a new Apple-designed A7 processor that has a 64-bit architecture. It runs a 64-bit version of iOS 7, which has 64-bit drivers. But why should anyone care about this? Does it really make it better than the 32-bit iPhone 5? Is the iPhone 5S twice as good? See: iPhone 5S vs iPhone 5C comparison review: what's the difference between iPhone 5S and iPhone 5C?
Bigger numbers sound better, but don't fall into this particular trap of thinking that 64-bits is necessarily better than 32-bits, or getting into a "My phone is better than your phone because it's 64-bit," argument. See also: Apple iPhone 5S review.
It's easiest to think of the processor as the heart of a mobile phone, or the engine that powers it. At the launch of the iPhone 5S, Apple made a big deal of the fact it has a 64-bit processor? There is no doubt that one day you will need a 64-bit processor in your smartphone, but you certainly don't need one today. Visit: The best phone you can buy in 2013?
You might therefore question why Apple has decided to switch to 64-bits. Cynical people say it is to give the iPhone 5S a unique selling point and it has something that no other phone has (yet).
The truth is that 64-bit is more than marketing puff: a 64-bit chip is used partly to improve performance and partly to prepare for the future. There's still a lot of life left in the 32-bit chip in your current phone, but the end is nigh.
64-bit vs 32-bit iPhone: Memory matters
PCs and Macs, Windows and OS X - everything is 64-bit these days. The reason is that there are limits on the amount of memory that a processor can access. A 16-bit processor can access 2^16 memory locations, a 32-bit processor can access 2^32 memory locations and a 64-bit processor can access 2^64 (that's 2 multiplied by itself 64 times - 2x2x2x2x...).
A 32-bit processor can access a maximum of 4GB of memory. This is one reason why desktop and laptop computers and their operating systems are all 64-bit these days. If they weren't, they would never be able to use more than 4GB of memory.
If you want 6- or 8GB of RAM in your PC or Mac, that's fine now, but a few years ago it wasn't possible. If you have less than 4GB of memory you may find the computer is sometimes slow and unresponsive. It's because it runs short of memory and it could do with more; these days we run more and more apps simultaneously and like to have scores of tabs open in our web browsers. They all require memory space, and there isn't always enough to go around.
Mobile phones and tablets are not yet struggling for memory in the same way as PCs and Macs are. Android phones and tablets typically have 1GB or 2GB of memory and the Samsung Galaxy Tab 3 is one of the few devices with 3GB.
Apple's iOS is more memory efficient and even though the iPhone's memory has doubled from 512MB in the 4/4S to 1GB in the 5/5S, it is well below the 4GB limit imposed by 32-bit processors. There's still room for apps and operating systems to grow and right now a 32-bit processor can address all the memory it needs.
As apps and mobile operating systems grow, there will come a day when 4GB of memory just isn't enough and then a 64-bit processor will be needed so phones can have more memory.
64-bit vs 32-bit iPhone: Performance gains
Breaking the 4GB memory barrier isn't the only reason for using a 64-bit processor and it can access and manipulate data in 64-bit chunks, which is twice as much as a 32-bit chip. If the processor needs to access a lot of data or do maths with really big numbers, it can do so more efficiently and this means that some apps will run faster, but they do have to be designed for 64-bit. It won't magically make 32-bit apps better and right now the million plus iOS apps in the store are 32-bit.
As far as performance goes, there will be losses as well as gains. Some 32-bit apps may be faster, but others might be no different or possibly slower on a 64-bit chip because it's working in sub-optimal 32-bit mode. Overall, though, there are usually more benefits. The main advantage of the A7 chip in Apple's iPhone 5S is that it's fast. Even in 32-bit mode running existing 32-bit apps, it's seriously quick.
64-bit vs 32-bit iPhone: apps
As we've said, every app is 32-bit at the moment, but don't worry because 64-bit processors can run them, so the iPhone 5S is backwards compatible with all existing apps. Apple is asking developers create new apps or rewrite old ones for 64-bit operation and submit them to the store, but it will take time.
Things don't work the other way around, however. A 32-bit processor can't run 64-bit apps and this means that there could be apps that work only on the iPhone 5S (and any other new 64-bit iOS devices that Apple launches).
Fortunately, that situation is unlikely given the sheer number of 32-bit iPhones and iPads out there. In fact, unless there is an advantage to running in 64-bit mode, a developer might stick with 32-bit apps because they run on every iPhone.
64-bit vs 32-bit iPhone: The future
Switching to a 64-bit processor removes the 4GB memory limit and boosts performance by enabling larger numbers and data to be manipulated by 64-bit apps. Today we live in a 32-bit world and where we want to be is 64-bit. The question is how to get there.
Apple has taken the first step, but the process will take several years. The iPhone 5S is simply the first step towards a future where phones are more powerful and have fewer limitations.
64-bit vs 32-bit Android phones
Will Samsung and other phone manufacturers follow Apple's lead? Yes, but whereas Apple has complete control over the design of the processor and operating system, Samsung and others must wait until Google gets around to making a 64-bit version of Android. The best guess is that this will be Android 5.0 in 2014. The odd thing is that Android needs 64-bit more than iOS does and devices like the Samsung Galaxy Note 3 at 3GB are already close to the 4GB limit.