Gold iPhone 5s top of the screen

Along with the iPhone 5s being a big seller, the new Apple handset has another not so welcome feature: its apps crash twice as much those on the iPhone 5c or iPhone 5.

The likely culprit: the iPhone 5s’s 64-bit A7 processor coupled with the 64-bit iOS 7 operating software and existing 32-bit apps. Apps running on the 64-bit iPhone 5s have a two percent crash rate.

That’s compared to just one percent for apps running on the iPhone 5c or iPhone 5, which use the previous-generation A6 chip and a 32-bit version of iOS 7…

Why is the iPhone 5s so vulnerable to app crashes?

The most probable reason is that developers had no time to check on the handset’s 64-bit hardware. By contrast, Apple released early test versions of iOS for 32-bit iPhones back in June, software flaw tracker Crittercism tells AllThingsD.

The company’s CEO described the problem as “inevitable” given Apple’s move to fully 64-bit hardware and software.

“Anytime there is new hardware or software release, we see issues,” Andrew Levy said. Levy pointed to when desktop PCs shifted to a 64-bit architecture, requiring developers to write new software.

The good news is that Apple is certainly aware of issues. Apple is doing a really good job of addressing these issues as they come up.

We previously detailed app crashes on the iPhone 5s, based on a growing thread on Apple’s support forums (here and here).

There’s one possible and reasonable explanation for all this.

Apple September 2013 event (iPhone 5s, 64-bit slide 002)

Transitioning existing 32-bits apps to 64-bit code brings with it increased memory usage that, unless managed carefully, can result in the increased memory consumption that can be detrimental to an app’s performance.

This is because iOS 7 on the iPhone 5s contains both 32-bit and 64-bit kernel, libraries and frameworks that load on demand, adding up to memory usage. When all apps running on the device are compiled for the 64-bit runtime, iOS 7 never loads the 32-bit versions of those libraries so the system uses less memory.

Unfortunately, app developers have only begun transitioning their code to the 64-bit platform so it’ll take a while until most App Store software is provided in the fat binary form that supports both 32-bit and 64-bit devices akin to universal iPhone/iPad app binaries.

Therefore, Apple states, “it is to everyone’s benefit that all apps running on 64-bit devices be compiled for the 64-bit runtime, especially apps that support background processing.”

Apple’s transition guide details porting apps to the new 64-bit architecture.

Here’s the dreaded ‘blue screen of death’ crashing an iPhone 5s.

Among the features introduced in iOS 7 is improved multitasking and Notification Center, the all-new Control Center and more. Since launching iOS 7 in late September, the company has issued two firmware updates fixing some of the early teething problems.

Now Apple is urging app developers to catch up by testing their apps on the 64-bit iPhone 5s. So far, most app updates have concerned themselves with only matching the cosmetic changes introduced with iOS 7.

What’s your experience with the iPhone 5s been so far?