Apple's Aggressive Backward Compatibility Drops

Apple's move to drop 32-bit app support with macOS Catalina in 2019 was a deliberate strategy to shed technical debt. Maintaining separate 32-bit and 64-bit libraries increased OS complexity, disk space usage, and memory consumption, as both sets of libraries would need to be loaded if even one 32-bit app was running. This transition simplified the codebase and aligned macOS with iOS, which had already transitioned to 64-bit only. The "app-ocalypse" caused significant disruption, as legacy software, including older versions of Microsoft Office and Adobe Photoshop, ceased to function. Some Adobe applications used 32-bit installers and licensing components, rendering them inoperable and even difficult to uninstall after the Catalina update. This forced users to find replacements or stick with an older OS, while developers who hadn't updated their apps in years were left behind. This wasn't Apple's first major compatibility break. The shift from PowerPC to Intel in 2006 was managed with the "Rosetta" translation layer, which was eventually dropped in OS X Lion (10.7). Similarly, the move from Intel to Apple Silicon in 2020 introduced Rosetta 2, an emulator that translates x86_64 instructions for ARM-based chips. Rosetta 2 demonstrates impressive performance, with benchmarks showing emulated x86 code achieving around 78-79% of the speed of native Apple Silicon applications. In some cases, the single-core performance of an M1 chip running an emulated app via Rosetta 2 still outperformed high-end Intel Macs. However, there is a performance penalty, and the initial launch of a translated application can be noticeably slower. In contrast, Microsoft has historically prioritized deep backward compatibility. 64-bit versions of Windows 10 can still run most 32-bit applications, and 32-bit versions of the OS even include a feature called NTVDM to support some 16-bit applications from the early 1990s. This commitment, however, can lead to a more complex and potentially slower file system. The Linux kernel also has a strong focus on Application Binary Interface (ABI) stability, with a general rule not to break userspace programs. This philosophy allows for rolling kernel updates without requiring a full OS reinstall. However, this stability primarily applies to the kernel itself, and dynamically linked user-space libraries can still introduce compatibility issues over time. Dropping older architectures allows Apple to enforce the use of modern frameworks and security features. For example, their Metal graphics acceleration technology only works with 64-bit applications. This approach forces the ecosystem forward, ensuring that new software takes full advantage of current hardware capabilities at the cost of leaving older, unmaintained software behind.