Exercise 1: Why AMD Created x86-64, Not Intel — Possible Solution
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WHY AMD IS CREDITED
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Per this chapter's own explanation, the 64-bit extension to the x86
architecture was designed by AMD, not Intel — a genuinely unusual
role reversal, since Intel had originated and driven the x86 line
since the 8086 in 1978. AMD's own approach, AMD64, extended the
EXISTING x86 instruction set with 64-bit capability while preserving
full backward compatibility with everything that already ran on
32-bit and 16-bit x86 chips.

INTEL'S OWN COMPETING APPROACH
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Intel's own answer to 64-bit computing was Itanium (IA-64) — per this
chapter, a COMPLETELY NEW architecture built from scratch, with no
backward compatibility with the existing x86 instruction set at all.
Running old x86 software on an Itanium chip required an entirely
separate compatibility layer rather than the CPU natively
understanding the old instructions the way it understood the new
ones.

WHY AMD'S APPROACH WON
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Per this chapter's own framing, AMD's design let existing 32-bit x86
software keep running completely unchanged on the new 64-bit chips,
while still gaining 64-bit capability for new software. Itanium
offered no such continuity — adopting it meant giving up compatibility
with the entire existing library of x86 software actually in use.
Given a choice between a clean break that discarded decades of
existing software investment and an extension that preserved it while
still delivering the needed 64-bit capability, the market chose
continuity. This is exactly the same underlying value — backward
compatibility — that this chapter's own broader "four decades of
accretion" theme has been describing throughout: preserving what
already worked, rather than replacing it, is what has repeatedly won
out across this entire architecture's history.

WHY THIS WORKS AS AN ANSWER
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It correctly credits AMD (not Intel) using the chapter's own stated
reasoning, names Intel's specific competing design (Itanium/IA-64) as
a genuine architectural alternative rather than a vague "Intel also
tried something," and explains the market outcome by tying it
directly to the chapter's own backward-compatibility theme rather
than treating AMD's win as unexplained luck.