Before we talk about why Intel Itanium failed,
we need to talk about something most people skip:
👉 instruction sets and CPU philosophy
Because Itanium didn’t just lose a market.
It lost a philosophical argument.
First: what is an instruction set (ISA)?
An Instruction Set Architecture (ISA) is the language a CPU understands.
Not C.
Not Java.
Not Python.
But the lowest-level commands like:
• load this value
• add these registers
• jump if condition fails
Examples:
• x86
• ARM
• RISC-V
Every operating system, compiler, and kernel is built around an ISA.
Change the ISA → rewrite everything.
RISC vs CISC (quick, practical explanation)
CISC Complex Instruction Set Computing
Example: x86
• Instructions do a lot
• Variable instruction length
• Decades of backward compatibility
• Hardware does heavy lifting at runtime
Pros:
• Older software keeps running
• Easier compiler targets
Cons:
• Complex CPU design
• Hard to reason about internally
RISC Reduced Instruction Set Computing
Examples: ARM, RISC-V
• Simple, fixed-size instructions
• Fewer instruction types
• Compiler handles complexity
• Hardware stays simpler
Pros:
• Efficient
• Predictable
• Scales well
Cons:
• Relies on good compilers
Where Itanium fits: neither RISC nor CISC (really)
Itanium introduced something else:
EPIC
EPIC = Explicitly Parallel Instruction Computing
The idea:
“Stop guessing at runtime.
Let the compiler explicitly tell the CPU what can run in parallel.”
So instead of the CPU dynamically:
• reordering instructions
• guessing dependencies
• speculating aggressively
The compiler:
• analyzes the program
• finds parallelism
• bundles instructions together
The CPU executes exactly what it’s told.
On paper?
Beautiful.
IA-64: Itanium’s instruction set
Itanium used IA-64, a completely new ISA.
Key characteristics:
• Very large instruction words
• Explicit parallel instruction bundles
• Massive register files
• Aggressive reliance on compile-time analysis
This makes IA-64:
• closer to RISC in simplicity
• but stricter than RISC
• and far less forgiving
If the compiler messes up → performance collapses.
Why EPIC struggled in the real world
The real world is messy.
• branches are unpredictable
• memory latency varies
• workloads change dynamically
• modern software is huge
Compilers cannot perfectly predict runtime behavior.
So CPUs like x86:
• speculate
• reorder dynamically
• recover from mistakes
Itanium couldn’t adapt well once compiled.
The design assumed:
“We can know enough ahead of time.”
Reality said:
“No, you can’t.”
Meanwhile… x86 cheated (successfully)
While Itanium bet everything on clean design,
x86-64 did something sneaky:
• kept the ugly CISC ISA
• translated instructions internally into RISC-like micro-ops
• used massive runtime scheduling logic
So x86 became:
• internally RISC-ish
• externally backward compatible
That hybrid approach won.
Not elegant.
But effective.
Who used Itanium anyway?
Only environments where:
• software was rewritten specifically for IA-64
• hardware costs didn’t matter
• long-term stability mattered more than ecosystem
Mostly running:
• HP-UX
• OpenVMS
• NonStop OS
Not general-purpose systems.
Not desktops.
Not startups.
Which operating systems supported IA-64?
Fully supported (historically)
• HP-UX
• OpenVMS
• NonStop OS
Partial / abandoned
• Linux
• Windows (briefly, then abandoned)
Once Windows dropped Itanium, the future was sealed.
The last Itanium processors
The final generation:
• Itanium 9700
• Released around 2017
• Minor refreshes only
• Officially discontinued in early 2020s
No successors.
No revival.
Who needs Itanium today?
Short answer: nobody new.
Long answer:
• legacy enterprise systems still running
• migrations planned but slow
• hardware kept alive via contracts
If you’re designing anything today:
• x86-64
• ARM
• RISC-V
All better choices.
The real lesson of Itanium
Itanium proves something uncomfortable:
The best architecture doesn’t always win.
The one that breaks the least stuff does.
Clean-slate designs are beautiful.
Backward compatibility is ugly.
But ugly survives.
Final thought
Itanium wasn’t a mistake.
It was a perfectly logical design built on a flawed assumption:
that software, compilers, and humans would adapt fast enough.
They didn’t.
And that’s why IA-64 is history and x86 is still here.
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