What is the difference between IA-64 and x86-64? Can normal windows be installed?

The fundamental difference between IA-64 and x86-64 is that they are entirely distinct, incompatible processor architectures born from different lineages and design philosophies. IA-64, also known as Itanium, was a joint venture between Intel and Hewlett-Packard to create a new 64-bit architecture based on Explicitly Parallel Instruction Computing (EPIC). It was a clean break from the past, designed to execute multiple instructions in parallel through compiler scheduling, aiming for high-performance computing in servers and workstations. In stark contrast, x86-64 (also called AMD64 or Intel 64) is a direct 64-bit extension of the ubiquitous x86 architecture pioneered by Intel and perfected by AMD. It maintains full backward compatibility with 32-bit x86 software while adding 64-bit registers and addressing, effectively evolving the existing ecosystem rather than replacing it. This lineage difference is the root of all subsequent incompatibilities, from the machine code they execute to the operating systems they can run.

Consequently, a normal consumer version of Windows designed for x86-64 systems cannot be installed on an IA-64 Itanium system, and vice versa. The operating system kernel, device drivers, and all application software are compiled for a specific instruction set architecture. Microsoft did produce specialized versions of Windows for IA-64, namely Windows XP 64-Bit Edition for Itanium-based Systems and later Windows Server 2008 for Itanium-Based Systems. However, these were niche, enterprise-focused products with extremely limited driver and application support, and Microsoft ended mainstream support for these versions years ago. The vast library of software written for the x86 and x86-64 platforms, including every mainstream version of Windows from XP onward, is completely non-functional on IA-64 hardware. The installation media itself would fail to boot or recognize the processor.

The market outcome of this architectural divergence was decisive. x86-64, by preserving the massive installed base of x86 software while offering a clear performance and memory addressability path, became the universal standard for everything from laptops to data centers. IA-64, despite its technical ambitions, failed to achieve significant market penetration outside certain high-end HP Integrity servers and specific legacy RISC-replacement scenarios. Its complexity, high cost, and poor performance on general-purpose code due to compiler challenges led to its commercial demise. Intel ceased Itanium production in 2021. Therefore, when encountering hardware today, it is almost certainly based on x86-64, which runs all modern 64-bit versions of Windows, Linux, and macOS. The practical implication is that users or administrators must verify their system's architecture; attempting to install a standard Windows distribution on discovered Itanium hardware is an exercise in futility, requiring the sourcing of long-discontinued, specialized operating system builds for which contemporary software support is virtually nonexistent.